Since 1994
members of the outdoor community have been trying to make sense of temperature
ratings for sleeping bags. Their purpose was to help consumers make wise
selections when they buy sleeping bags. Static tests were developed but they
are of little value to the consumer. It was determined that consumer knowledge
and education would provide the best service for the consumer.
This somewhat dry, technical document
is cram packed with detailed information about sleeping bags, how they work,
what to look for and how to buy them. This is your ticket to a well considered
sleeping bag selection and a warm comfortable nights sleep.
Table Of Contents
A)
What is a thermal insulator and how does it work? (R. Parry and L. McCullough)
B) Design features influencing bag
performance (J. Maggio and G. Foweraker)
C) How to keep warm in a sleeping bag (H.
Heyburn and A. Lee)
a.
a.
Role
of metabolism and body mass
b.
b.
Diet
(protein, carbohydrates, sugars, hot beverage)
c.
c.
Age/Physical
condition
a.
. Ground and ground
pad, conductive surfaces
b.
a.
Cots,
hammocks and convective areas
c.
b.
Tent
d.
c.
Clothing
a.
. Campsite
selection/protection from the elements
b.
a.
Bag
conditioning in the field
a.
. Revitalize in home
dryer before trip
b.
a.
Keeping
your bag clean
D) How to choose a sleeping bag (P.
Hickner and S. Klien)
a. Time of year, range
of conditions, environment. Single/Multi-season range of use
b.
Type
of camping
c.
How
much use/durability
a.
Size and Shape
b.
Fit
c.
Weight, compressibility
d.
Price, budget
E) How to care for a sleeping bag (F.
Dieter and E. Weidler and P. Hickner)
A) What is a thermal insulator and how does it work?
(R. Parry and L. McCullough)
INTRODUCTION
What
do temperature ratings really mean? People shopping for a sleeping bag must
understand that the ratings given by a manufacturer are conditional. They need
to understand all the factors involved for keeping warm. The bag is only an
insulator, not a heat generator. A manufacturer can only estimate the
temperature rating of a bag and some may be more connservative than others. As
a shopper you must carefully evaluate your own metabolism and tolerance of
cold. You must decide how much margin to leave for nights you are hungry, wet,
sick, injured, exhausted, disheartened, or caught without a tent. The thickness
of the insulating layer generally determines the warmth of a bag, but different
types of insulation require a different thickness.
Heat Production in the Body The human body generates heat as a by-product of
metabolism (the chemical processes necessary for essential body functions). A
person’s heat production is primarily dependent upon their basal
metabolic rate and activity level. Some muscular activity
generates mechanical work, and the remaining activity generates excess heat
energy. Therefore, the higher the activity level, the higher the body heat
production.
Body Heat Balance A person is most comfortable when the excess heat
produced by the body is exactly the same as the heat lost to the environment.
When the rate of heat production is equal to the rate of heat loss, the person
is said to be in heat balance. Excessive heat loss to a cold
environment will cause the body temperature to decline and may lead to
hypothermia. Although the body can tolerate a heat deficit for a short period
of time, eventually the heat must be regained to stay healthy.
Factors Affecting Thermal Comfort (Heat Balance) There are three major factors that can be adjusted to
maintain body heat balance and thermal comfort:
1.
human activity level determines amount of metabolic heat production.
2.
environmental conditions determine amount of body heat loss.
3.
insulation systems including clothing and sleeping bags determine
amount of heat loss.
In
addition, the amount of time that the person is exposed
to environmental conditions, while covered with a given amount of insulation is
important. You may be able to tolerate a cold environment for a short period of
time (allowing for a small amount of heat debt), but eventually the thermal
imbalance would cause discomfort and health problems.
Heat Flow From the Body to the Environment Heat is dissipated from the skin surface by conduction,
convection, and radiation. These mechanisms of heat
energy movement are collectively referred to as sensible or dry
modes of heat transfer. Heat is also removed by the evaporation
of sweat from the skin surface, called evaporative or latent heat
transfer. Sleeping and resting individuals lose about 25% of their heat
through respiration (a combination of convection and evaporation) and
insensible perspiration from the skin (evaporation). The remaining 75% is dry
heat loss from the body surface.
Heat
always flows from an area of high temperature to an area of low temperature. Therefore,
heat is usually transferred from a warm body to a cooler environment. The rate
at which this heat flows depends upon the differential between the two
temperatures; the greater the temperature gradient, the faster the heat flow.
The heat transferred from the body decreases as the amount of insulation
between the body and the environment increases. The heat flow also increases as
the amount of surface area increases.
Vasoconstriction
of blood vessels near the skin reduces heat loss from warm blood and reduces
the temperature gradient between the skin surface and the cold environment.
Blood vessels in the head however, do not constrict. Shivering is a mechanism
the body uses to warm itself.
2) Insulation - Dead air space
Thermal Insulators and How They Work A thermal insulator can be defined as a device or
condition that regulates or resists the transfer of heat energy from one body
or environment to another. A good insulation system must be effective at
stopping body heat loss via conduction, convection, and radiation.
Most
insulation systems that are used to reduce heat loss from the body are made of
textile structures that are mixtures of fiber and air. Fiber dominates by
weight and visibility, whereas air dominates by volume. The fibers obstruct the
flow of radiant heat and stabilize the air in the textile structure to minimize
convection heat losses. The still air also reduces conduction losses since air
has a lower conductivity than fibers.
The
simplest sleeping bag insulation system is usually a multi-component structure
consisting of an outer shell fabric, an insulating material, and liner fabric.
Shell Fabrics. The shell fabrics should be wind resistant to prevent
cold moving air from penetrating the bag and increasing convection heat loss.
Shells should be water resistant to prevent precipitation from penetrating the
bag, displacing still air, and increasing conduction heat loss. Shell fabrics
should also be strong, durable, and soil resistant. To achieve these
properties, the fabrics are generally tightly woven in a thin structure made of
nylon or other fibers. These high density structures help to block radiation
heat loss from the body also. These materials should allow water vapor (i.e.,
the evaporated sweat from your body) to escape to the environment.
Insulation Materials. The typical insulation materials that are used in
sleeping bags include natural fills (down and feathers) and battings of
synthetic fibers (polyester fiberfill and polyester/olefin fiberfills). These
insulating materials are sandwiched between the shell and lining fabrics using
a variety of methods (enclosed channels, layers, baffles). Fiber manufacturers
can vary certain fiber characteristics to improve the thermal performance of a
batting (increase its insulation per unit weight). They can vary the fiber
diameter ( denier), fiber length (from short staple lengths to long, continuous
filaments), the shape of the fiber cross section, fiber crimp, and the size and
shape of holes or voids inside the fiber. Batting producers can vary the
thickness, density, and weight of the fiberfill also.
Effective
insulators need to be thick and resilient. The filling materials need to
maintain their thickness over time and recover from compression during use. The
thicker the insulation, the more resistance to heat transfer it will provide.
This is because thicker structures trap more still air and lower conduction
heat losses. If the density of the filling material is too low the air will not
be stabilized and convection losses will increase. Low density filling
materials also allow radiation losses to occur. Battings made with microfibers
( fibers with a denier less than 1) tend to reflect, scatter, absorb and
re-emit more radiant energy as compared to the mid-denier and larger fibers.
This
mode of heat transfer involves direct physical contact. A body or material can
conduct heat energy to another substance when there is a temperature difference
between the two. When in contact, the transfer of thermal energy involves the
motion and collision of the atoms and molecules of these materials. For
example, when you sit on a cold surface like a rock, heat flows from your body
surface to the rock until equilibrium is reached. Another example of conduction
involves the transfer of heat energy from your skin surface to the still air
layer on the body surface, and to the still air trapped within fabric layers
and between fabric layers in your clothing. However, air has a very low thermal
capacity and is a much better insulator (poorer conductor) than the fibers and
other materials that make up clothing, bedding, and sleeping bag systems.
Water, on the other hand, conducts heat much faster than fibers or air. For
example, if you were immersed in 50°F water instead of 50°F air, you would lose
heat much faster in the water due to conduction.
The
convective mode of heat flow transfers heat by moving large aggregates of
molecules. The motion of these large aggregates, usually gases or liquids, is driven
by a temperature gradient. For example, pouring cold water into a hot cup of
coffee will transfer heat by convection as the two liquids mix. There are two
types of convection: natural convection and forced convection.
In
most cases, gravity is the mixing force in natural convection. The interaction
of hot and cold air around the human body is a good example. Cold air is at a
lower chaotic level (lower temperature) than hot air. Thus, there are more cold
air molecules per unit area than hot air molecules at the same pressure. So the
cold air will weigh more than the hot air. The still air next to your body will
be first warmed by conduction. Then this hot air will rise, and the cold air
from the cool surrounding environment will fall. As your body warms the next
layer of air, the process repeats itself.
Forced
convection can be mechanical (a fan, or forced air heating system can be the
mixing force), or it can be caused in nature by differences in pressure (wind).
Forced convection can be an important factor when a person is outdoors. The
blowing of cold air against your body can accelerate the heat transfer process
making you feel colder faster. Convection losses can also be caused by body
movement in a large fitting sleeping bag or in loose fitting clothing. Cold air
mixes with the warm air inside the bag or garment layers, causing an increase
in body heat loss.
This
mode of heat transfer is the transfer of heat energy by means of
electromagnetic waves. The human body is constantly giving off heat in the form
of radiant energy. This energy can be reflected, absorbed, and converted into
other forms of heat energy, or transmitted unchanged to objects in the
environment. This transfer does not require a physical medium like air, so it
can take place across a vacuum. In a cold environment, where the temperature is
lower than that of your body, there will be a continuous interchange of radiant
energy. The warmer body will radiate more energy than it will absorb, and the
environment will absorb more than it radiates.
The
evaporation of perspiration from your skin surface to the environment is a
major mechanism for heat loss from the body, particularly in warm environments
and/or at high activity levels. Heat energy is taken from your body as the
liquid water is converted to water vapor.
Perspiration
generated by your body needs to be evaporated from the skin surface and
transferred through garment layers (and sleeping bag layers) to the
environment. If the water vapor cannot escape, the relative humidity near your
skin will increase, and you will experience a sensation of clamminess. If a
clothing or sleeping bag system is ineffective at allowing the moisture to
escape, or if the relative humidity of the environment is high, the "microclimate"
near the skin will become saturated and eventually the moisture will condense
in the textile layers and on the skin. Under these conditions, you will become
very uncomfortable. In extreme conditions, where a considerable amount of
moisture condenses and builds up in the insulating layers, conduction heat
transfer through the layers will increase. This is because water is a much
better conductor of heat than the fibers of the insulating layers.
In
other cases, the use of a vapor barier liner (VBL) against the skin prevents
evaporative cooling and also prevents moisture from getting into a sleeping
bags insulation. VBL's are used in extreme cold situations when there is a
premium on survival!
B) Design features influencing bag performance (J.
Maggio and G. Foweraker)
INTRODUCTION
Before
searching for a sleeping bag it is important to define the exact needs you
expect the bag to meet. These needs must be realistic so the help of a trained
sales person is helpful. Setting expectations that are impractical will only
lead to disappointment when the wrong bag is chosen. Remember not one sleeping
bag will do everything. So don't be tempted to get a bag that is too warm (ie.
heavier, bulkier, hotter), when most of your use may be in warmer summer
conditions.
It
is important to understand the function of the features that can be built into
a bag. Not all bags need to be full featured. By understanding how these
features work then you can decide which ones are desirable for the sleeping bag
you need. Buy only those bag features you need to meet your intended purpose.
This could save you money and weight. Features that are useful for colder
temperatures may have no place in a summer weight bag. Bags that are
"versatile" compromise in other areas.
Be
sure though, to get all the features you need for your bag to preform to your
expectations.
This
is an insulated tube running parallel to and alongside the zipper that blocks
heat loss thru the teeth of the zipper. Otherwise, this area would have a long
uninsulated seam running the length of the bag. Ideally, the tube is sewn only
to the lining material, since sewing through the bag creates a cold spot.
Depending
upon the temperature requirements of the bag, this tube may be thickly
insulated, a simple flap of fabric, or absent altogether. For cold weather bag,
two thickly filled draft tubes may be necessary. In some cases the tube may be
sewn to the bottom half of the zipper, this could be less desirable if the tube
is scrunched down during the night exposing the cold zipper. A tube hanging
from the top won't do this. You may find draft tubes with a stiffener to help
prevent zipper snags. The draft tube may be attached to the bag with a single
sewn through seam, or it may be attached with two seams so that there is no
cold seam. The choice of construction depends on the temperature requirements
of the bag. Any one of these constructions is acceptable as long as they are
not mismatched to the temperature requirements of the bag.
2) Collar, Draft Collar, Neck Yoke
The
collar is an insulated tube covering your throat and shoulders. It is intended
to either lay across the top of your neck or to completely encircle it. It may
be a flap of fabric or an insulated tube. And its variations in construction
are similar to those of the draft tube. The purpose of the collar is to prevent
heat loss from around the neck. Some of this heat loss is due to the
"bellows effect" that is caused while moving around inside the bag.
Warm air can be pushed out and cold air sucked in as the volume inside the bag
changes. The collar acts as a dam to help slow this loss. Collars are more
important on colder weather bags.
3) Shifting Insulation, Loft Distribution 60/40,
Amount of Loft
Down
bags may be built with continuous baffles These are uninterrupted tunnels that
run from the top of the bag to the bottom. They allow you to fine tune the
warmth of the bag by redistributing insulation from top to bottom and vise
versa. However, continuous baffles can allow down to shift on its own, so
periodic shake-ups may be needed. Other bags are built with a side-block
baffle. This is a netting wall running the length of the bag on the side
opposite the zipper to hold the down in place. This baffle helps to preserve
the generally 60%-40% fill ratio of top to bottom of a sleeping bag. More fill
is generally placed into the top of a bag since heat rises and since the
insulation value in the bottom of the bag is reduced due to compression. Winter
bags should have a side-block baffle.
4) Sewn through seams and Baffles
Sewn-through
seams are the easiest, and lowest cost construction for a sleeping bag. The
insulation is sandwiched between the inner liner and the outer shell and the
seams sewn through all three layers. Since each seam line is a thin,
unprotected, uninsulated cold seam, this method should only be used for warm
weather bags. Not only will these sewn together seams help lose excess heat,
but the bag can be constructed much lighter. However, in colder temperatures
sewn thru seams become cold spots and that’s why "two" and
"three" season bags bags are constructed with sewn in baffles. In
this case the inner and outer shells are connected by a piece of baffling material
that separates the two shells. In that way the insulation keeps the two shells
apart throughout the entire length of the bag.
Up
to 50% of your body's heat can be lost through your head, an effective hood is a
weight efficient way of improving a bag's warmth. Better hoods are tailored and
can be subtly adjusted to move with you in your sleep. Hoods should be able to
draw up and close to a 3" opening, provide room for wearing a hat, and
should feel comfortable against the face. Semi-rectangular bags may not have
hoods and depending upon their intended use this is not necessarily a drawback.
Protruding
at right angles to the rest of the body, your feet will tend to crush the upper
insulation of the sleeping bag. Better designed mummy bags are flared and
boxed, and have more insulation in the foot area. A less tailored equivalent
feature in a barrel bag is called a foot circle.
7) Air space within a bag/cold spots
Other
things being equal, the more snugly a bag fits, the more thermally efficient it
is, since your body will heat a smaller volume between you and your bag.
However, the bag must be roomy enough to allow a good night's sleep. The amount
of space needed is a personal judgment.
8) Off-set quilting/shingles/etc.
Off-set
quilting is essentially two layers of sewn through construction (see above)
arranged so that the tubes fill in the uninsulated valleys in one another. Many
synthetic insulations are made in sheets (called batts) which can be attached
directly to the bag fabric in overlapping layers, like the shingles on a roof.
Even
at rest, the human body gives off moisture which can degrade the warmth of your
sleeping bag. Bag shells may be made of water resistant or waterproof fabrics
but the fabrics must remain breathable. Bags may feature insulations which
retain a greater degree of warmth when damp, or which may dispurse moisture so
it can evaporate more easily.
The
inner shell fabric of a bag should be cut narrower than the outer shell fabric
to allow the insulation to fluff up to its maximum volume and to prevent the
inner shell from contacting the outer shell which would create a cold spot.
This construction is common in mummy bags, but not so with rectangular bags
which are often required to open up and lie flat.
The
choice of shell fabric and finishing affects the weight, water repellency,
comfort, cost, durability and longevity of a sleeping bag. There is no
universal consensus on the best fabric. Often bags will have a tightly woven
shell with a DWR (Durable Water Repellent) finish. High thread count fabrics
(270+ per square inch) are designed to minimize down leakage and to improve
wind resistance. Any sign of down or fiber coming through the fabric is cause
for suspicion that the weave may not be tight enough.
Nylon
and Polyester are the most common shell fabrics. You can find bags made with
fabrics as heavy as 2.2 oz./yd. and as light as 1 ounce. Lighter fabrics may
not be as durable or as down proof but with careful use may suit your extreme
lightweight needs for many years. Nylons are often calendered to make them more
downproof and fiberproof.
Polyester
is a softer fiber than nylon, and especially when woven with microfiber yarns,
has a nice hand and drape. It also absorbs less water. Polyester holds a DWR
finish better than nylon, but it's not as strong for the same weight.When
compared to natural fibers, nylons and polyesters are stronger, absorb less
water and dry more easily.
Cotton
is comfortable next to the skin and is preferred by people who are sensitive to
synthetic materials. It is often woven into flannel and used for general
purpose sleeping bags. Cotton shelled sleeping bags pretty much disappeared
twenty five years ago. Per unit weight, cotton is not as strong as nylon and
polyester, absorbs moisture easily, and is hard to dry.
PTFE
(polytetraflouro-ethylene) laminates are waterproof/breathable shells made with
a shell fabric laminated to an expanded PTFE membrane (originally patented as
Gore-Tex™). They have proven very effective in keeping sleeping bag insulations
dry. This laminate is wind-proof and makes a bag warmer in many conditions.
This fabric is often used in the outer shells of more technical bags,
especially those insulated with down. There are a varity of expanded PTFE
laminates being offered for bag shells. A PTFE laminate can add to the cost of
a bag. As technology improves, the breathability of waterproof/breathable
polyurethane-coated fabrics may provide a lower cost alternative to PTFE
laminates.
Inside
liner fabrics are generally a light weight nylon, usually lighter in weight
than the shell fabric. In cases where gear may be stored at the foot of a bag
during cold weather use, a heavier fabric may be used in that location.
Though
synthetic fills are constantly improving, down remains the leader in
warmth-for-weight, compressibility, and resilience. Down is the fluffy
undercoating of ducks and geese, located just beneath their outer feathers.
Down insulation breaths well, and drapes itself over your body reducing
internal air spaces. It is also more comfortable over a wider range of
temperatures.
Although
down has a high initial cost, because its useful life is measured in decades
rather than years, it offers superb value in the long term.
Down
is graded for quality according to the number of cubic inches one ounce of down
will displace when under a controlled pressure. This displacement is referred
to as "fill power"; 400-450 fill down is fair, 500-575 fill is good,
600 and above is excellent. Many factors affect fill power. As a result a
laboratory will condition a down sample for several days in order to stabilize
it, and still they can expect a 10% variation in their results. Since few
consumers are equipped to scientifically test down fill, your best protection
is to buy established brand names from reputable retailers.
Synthetic
fills are non-allergenic, retain more of their insulative properties when wet,
and have a lower initial cost than down. Combine these benefits with ever
improving warmth-for-weight, and synthetics become a viable, and for some
users, preferable alternative to down.
Synthetic
insulations are extruded polymers, essentially plastic threads. These threads
may be either continuous filament (a single long strand) or short staples,
pieces 1.5 to 4 inches long. Either type may be made with hollow threads. The
hollow interior reduces weight, and traps air for insulation. Some synthetics
are microfibres with textured surfaces that reduce air circulation and increase
warmth.
More
technical bags are designed for maximum lightness and compressibility, and some
loss of thermal effectiveness is expected over time. Relatively bulky, heavy
and durable insulations are used for applications where weight is less
critical. Most synthetic fills keep their loft when wet. For this reason, many
will consider synthetics if there is any chance of getting wet. The wide price
range virtually assures you of finding a bag warm enough at a price you can
afford.
All
bags will yield poor performance when wet. The best advice is 1) keep them dry,
and 2) evaluate the number of times your bag has gotten wet in the past,
(usually zero). Bags used on paddling trips are easily protected with a dry
bag. and tents generally cover bad weather. If your tent leaks, fix the tent!
All bags should be air dried during the daytime hours. Also, most shell fabrics
are treated with a DWR. Keeping your bag's DWR maintained will improve its
performance. It is not usually difficult to keep water problems to a minimum.
If
bags are of similar design have zippers the same size and roughly the same
length, they can often be zipped together. Mated bags allow a warmer sleeper to
share heat with a colder sleeper, and in addition, each partner can select a
warmer or colder bag for their side. If you are mating barrel or rectangular
bags, you can carry bags of different warmths, putting the thicker one on top
of both of you in colder weather and vise-versa. However this system is less
efficient than separate bags, since there are more gaps and voids and the
movements of two people pushing out warm air.
15) Size and volume of bag-length and width
Sleeping
bags with lower internal volume are more efficient since there is less air
inside the bag to heat up. First the air inside the bag then the dead air
within the insulation must warm up before the bag will begin to insulate. Lower
volume bags heat up sooner and insulate sooner. However, comfort in regards to
claustrophobia is also a factor, so it is individual preference how much room
you may need.
C) How to keep warm in a sleeping bag (H. Heyburn and
A. Lee)
INTRODUCTION
Even
during summer nights cold weather can be expected. In mountainous areas, cold
is even more common. Knowing how to properly use a sleeping bag can make the
difference between a cold miserable night or a comfortable restful sleep till
morning.
Keeping
warm in a sleeping bag is divided into three main parts; human components,
environmental components, and your sleep system components.
Remember,
your sleeping bag does not produce heat. It is only an insulator that slows
heat being lost from your body. In cold conditions it is important to start the
night warm. You will sleep comfortably if you maximize your body’s heat
production and minimize heat loss.
a) Role of metabolism and body mass
The
human components that directly affect how warm you will be is based on your
metabolism. Taking a short walk or light exercise is a way to increase
metabolism by getting your muscles to generate heat. But do not work to the
point that you will begin to sweat, this could cause the inside of your bag to
become damp. Your muscles are responsible for generating heat, and don't expect
fat to be a good insulator. Therefore being in good shape is important for a
warm nights rest.
b) Diet (protein, carbohydrates, sugars, hot beverage)
It
is important to have enough to eat and drink before going to sleep. Poor food
and water intake during the heavy exertion associated with backpacking can
disrupt your body's metabolism and prevent it from heating your body. Your body
will burn fats throughout the night and generate heat. A hot beverage with
sugar just before retiring will warm you up so that your bag heats quicker.
Sweet food will boost your metabolism and warm your sleeping bag's insulation.
c) Age/Physical condition
Your
mental state along with your physical condition or level of fatigue will
contribute to how well you will sleep. Both your age and physical condition
will affect your metabolism. In general older people or people in
"poor" health will have a lower metabolic rate and therefore , they
will have a harder time warming their bag. In this case they should buy a
warmer rated bag.
2) System components/Auxiliary products
Your
sleep system includes more than just your sleeping bag. Other components that
affect your warmth are a sleeping pad, ground cloth, bivy sack or tent. All of
these items will increase your chances of having a warm night’s sleep by
reducing the amount of heat lost through convection and conduction.
a) Ground and ground pad, conductive surfaces
Using
a ground pad made with an insulative foam will help prevent conductive heat
loss between you and the ground. Polymers are a major building block of foam
and polymer is a good conductor of heat. It's been found that open cell foam is
a better insulator than closed cell foam because open cell contains less
polymer. For winter use, an insulative pad with an R value greater than 2 is
recommended.
b) Cots, hammocks and convective areas
The
use of a cot or hammock presents a unique situation. Many people believe that a
foam pad is just meant to provide a soft surface to sleep on, and therefore
they elect not to use one when using a cot or hammock. The result is that there
is very little insulation under the sleeper and air currents moving under the user
will rob heat.
c) Tent
The
use of a tent or bivy sack helps to create another layer of dead air space and
helps to reduce convective heat loss. Lab tests show up to a 10° F benefit by
using one of these.
d) Clothing
Since
the majority of heat is lost from your head, wearing a hat when you turn in,
will help increase the chances of having a nice warm relaxing night. The amount
of dry clothing layers you have on will also help keep you warm. The more
clothing layers, the more insulation, leading to a warmer sleep solution. But
do not allow the additional clothing to compress the insulation of the sleeping
bag. The theory that sleeping naked is warmer, may be fun, but it is untrue.
3) Human/Environment Interaction
a) Campsite selection/protection from the elements
The
environmental components of keeping warm in a sleeping bag are critical to
prevent a good evening from turning into a nightmare. Avoid camping in low
areas where cold air collects. Moving air causes convective heat loss so camp
sites should be sheltered from the wind. Be prepared for high elevations to
cool quicker when the sun sets or goes behind clouds.
b) Bag conditioning in the field
It
is best to set camp early enough for you to prepare your sleeping site. It is
suggested you open up your sleeping bag as soon as you can. Giving your bag as
much time as possible to fully loft will maximize its insulative value. Pull
your bag out of its sack and shake it and fluff it to get air mixed into the
insulation. Do this several times before retiring.
4) Manipulating bag features, adjusting insulation,
controlling heat loss
Some
bags offer the possibility of adjusting and distributing insulation. Some
models of down bags for instance are constructed with continuous baffles. By
distributing the insulation from top to bottom you can better control the
insulative value of your bag and tailor your needs to the given climate. In
warmer weather move the insulation to the bottom of the bag and when you find
the weather cooler than you expected, move more of the insulation on top of
you. Use your cord lock to snug the hood about your face, or distribute the
inside hood material to create a hood ruff. By learning to minipulate the
features of your bag you can better control heat loss.
a) Revitalize in home dryer before trip
It
is not a bad idea to put your bag into a dryer set to low heat before leaving
on a trip. The tumbling will reloft the bag and at the same time, the heat will
drive out any moisture that may have accumulated during storage. This works for
both down and synthetic sleeping bags.
b) Keeping your bag clean
By
keeping your bag clean its loft will be maintained. Using a ground cloth under
your bag will protect the shell from abrasion, dirt and ground moisture. You
may also use lightweight underwear and socks to keep body oils and sweat out of
your bag. Think of your underwear as sheets on a bed. That's why you don't
often launder your mattress.
Be
aware of a sleeping bags life expectancy. Shell fabrics and insulations
deteriorate over time at different rates. Exposure to UV radiation may speed up
some deterioration. Comparing current loft to the loft when the bag was new
will provide an indication of how much the insulation has deteriorated. Washing
a sleeping bag may improve loft. Down bags often have the longest life spans.
D) How to choose a sleeping bag (P. Hickner and S.
Klien)
INTRODUCTION
The
best advise is to learn all you can. Designs and materials change, and you may
find that your knowledge is out of date.
Try
these sources of information:
Equipment
reviews from the library or internet services. Remember that reviewers are not
infallible, and may have biases. Manufacturers catalogs are very helpful. Read
the text and specifications carefully. Speak with guides and other mountain
professionals. People with specialized knowledge are usually happy to share it.
Outdoor
store sales people can be a wealth of knowledge. Choose your store carefully
after you have read some catalogs. Visit two or three stores for a more varied
opinion. Ask about brands that the store does not carry. It is easier to learn
negatives from someone who does not sell the product.
You
will have to consider price, temperature range, weight, size, water resistance,
durability, and compressibility as well as, zipper placement, compatibility
with other bags, and even the feel of the fabric.
Carefully
determine your needs. But be realistic about how you will use your bag. You
probably will never find a bag that meets all your needs and wants, so first
decide where you will not compromise and where you can.
a) Time of year, range of conditions, environment.
Single/Multi-season range of use
Carefully
consider the temperature range to be covered. If the range is wider than any
one bag can cover, you need to decide which end of the range is most important
to you. Buy the bag for the weather you will MOST often encounter. You may be
able to add extra clothing, use a bag liner, a vest, or an over bag, to extend
the range of your bag. That will save you expense, spare you carrying extra
weight, and keep you from sweating on warm nights. Do not use temperature
ratings to cross reference between companies. There are currently NO accepted
standards between manufacturers for rating a bag in degrees. Part of the
problem is that everyone has their own metabolic rate.
Backpackers
in the mountains can encounter variable conditions even in the summer, and you
will need to be prepared for all possibilities. You could buy a Two-season, or
Three-season bag to cover a wider temperature range. If you're only a fair
weather summer camper, you may get a single season summer bag with a higher
temperature rating. On the other hand, you may be the extreme winter
mountaineer. Then you would best be served with a single season winter bag with
a low temperature rating. These bags are only useful for cold conditions so
don't be tempted to get a winter bag for all your neeeds.
b) Type of camping
Car
camping - Weight and volume aren't really an issue. The bag of choice could be
a rectangular or semi-rectangular bag . If you want more comfort, you could
choose a bag with a cotton/polyester liner.
Backpacking
- Lightweight and low volume would be important. A mummy style bag would be
most practical.
Bicycle
camping - Lightweight and low volume would be important. A mummy style bag
would be most practical.
Kayak
or canoe camping - Low volume for storage, usually inside a dry bag.
c) How much use/durability
Determine
how much you will use your bag. You may need to consider a more durable bag or
you may evaluate your skill level for caring for a bag. Durability can add cost
and weight, so evaluate your needs and skills carefully.
a) Size and Shape
Mummy
bags are the most efficient. Many mummy bags are available in wide girths so
that you do not have to be squeezed in a mummy bag. People who car camp or use
a sleeping bag to double as a quilt should consider a rectangular bag.
Semi-rectangular bags hold appeal for those who feel constrained in a mummy bag
and want some kicking around room. They also make good zip together
combinations, either with another semi-rectangular bag or a ground sheet
combination.
b) Fit
For
most people, the smallest size that is comfortable is the right size. A smaller
bag will warm up faster and save weight. You should try on a few bags to get a
good sense of size. If you have a bag already, measure it and compare it to
prospective bags. Be aware that there is some inconsistency in published
measurements. Measure for yourself if you have the opportunity. Remember that
bags with equal shoulder and foot measurements can have different contours in
between. Decide if you need to leave room for wearing extra clothing. Consider
if you want to leave room at the bottom of the bag for clothing, boot liners,
and to keep water bottles warm.
c) Weight, compressibility
Narrow
cut bags are lighter and more compressible than wider cut bags. Wider bags use
up more
materials
in their construction and so are often more expensive than other bags at the
same temperature rating. Many hikers make weight and compressibility the
primary consideration in choosing a bag, but you should recognize that a
comfortable sleep is worth hauling a few extra ounces up the trail.
d) Price, budget
Dream
of the perfect bag if you want, but limit your search to what you can afford.
We all started with equipment that was barely adequate and we had a great time
anyway. But be aware of what money will buy, if you need it you'll have to pay
for it. You won't get something for nothing. When considering cost consider
also longevity and quality of the product. Reliability also costs more. Cheaper
products may have to be replaced more often and won't magically keep you warm.
Learn the principles first then know your compromises when you make your
decision. In most cases, there will be a bag in your price range that can fit
your needs.
3) Be aware of acceptable levels of variation and
construction
a) Materials
There
are many different shell fabrics available for sleeping bags. Understand the
trade offs for different features that may make a bag "better" but
only for a specific use. As water resistance increases, breathability often
decreases. "Bearding" may result when a shell fabric doesn't have a
high thread count or tight weave to contain the insulation and the fibers
migrate through the surface of the fabric. Make sure the fabric has enough
integrity to hold up along the sewn seams. Pull at the side seams lightly to
see if the fabric is separating and allowing seam slippage. Make sure the
zipper opens and closes easily. Understand the variations in down fill power and
how it is derived and used. Learn as much as possible about the materials in
your bag so that you can better understand what to expect.
b) Workmanship and Quality
Stitching
should be close and tight. Loose stitching will snag and shorten the life of a
bag. Ask if the internal seams are stabilized to prevent unraveling. Learn to
look at the overall construction, features and finish of the bag to determine
its quality.
c) Warranty
Look
for a lifetime warranty on materials and workmanship for an indication that the
manufacturer believes in the quality of its products. But recognise that
"Lifetime" will usually apply to the product and not necessarily your
good health.
E) How to care for a sleeping bag (F. Dieter and E.
Weidler and P. Hickner)
Always
read and follow the manufacturer's care instructions. Different fabrics,
insulations or bags may require different handling techniques. Sleeping bags
are made to be stuffed hundreds, even thousands, of times without damage.
Improper stuffing, however, may shorten the life of your bag. Use a larger
stuff sack if space is not your primary consideration. Recognize that frequent
use of compression sacks will take a toll on the loft of the bag. Also , a
larger but softer stuff sack is easier to pack around than a solid hard
cylinder. Always make sure you are stuffing the bag evenly. Push the sleeping
bag firmly into the bottom of the stuff sack from the outset so that the bottom
of the stuff sack is stuffed as tightly as the top.
Avoid
leaving a stuffed polyester bag in a hot car. Leave it unstuffed in the trunk
(the trunk of a closed car parked in the sun is much cooler than the passenger
compartment).
2) While in storage (air bag after use)
Store
your bag in a cool, dry place that has a fairly constant temperature (between
65 and 80 degrees). Never store your bag compressed for long periods of time.
Bags should be hung or stored in a large, breathable storage sack or pillow
case. They should never be stored for long periods in anything watertight as
condensation can occur inside the bag and result in mildew. You may wish to
tumble dry your bag in the dryer on low heat for 10 minutes before storing,
even if it feels dry.
Do
not expose your bag to sunlight for long periods as UV radiation can degrade
the nylon.
Do
not expect all bags to be cleaned the same way. Different synthetic fills may
require special handling as well as different down products may have prefered
methods for cleaning. Again, refer to the manufacturer's recommendations. In
most cases washing is the only acceptable method for cleaning a sleeping bag.
Dry cleaning will damage both down and synthetic bags. Body oils, hair oils,
lotions, and cosmetics are all acidic and will cause down or synthetic
insulation to decompose and lose it’s loft. A bag should be cleaned when it has
begun to lose loft or becomes discolored due to oil accumulation.
Soap
should be your first choice for stain removal. You can use cleaning solvents to
spot-treat tough stains, sap, or tar. You may want to experiment on a very
small area to be certain that it doesn’t damage the fabric. Try to move the
down or insulation away from the spot you are cleaning and use an absorbent
cloth on the reverse side. PTFE membrane laminates do not require different
treatments than other fabrics.
It
is best to wash your bag yourself by following the manufacturers detailed
cleaning instructions. Otherwise, take you bag to a professional laundry
experienced with down or synthetic insulated products. If no care instructions
exist, hand wash or use a front loading machine without an agitator. Tumble dry
on low heat checking frequently for overheating. A light soap is fine for
synthetic bags, but a special down soap, available at your local outdoor shop,
is best for down bags. Do not expect these down soaps to remove all stains
since they are mild and not the most powerful stain removers. Make sure your
bag is completely dry before storing.
During
use in the field it is important to air dry you bag during the day. This will
dry out and remove perspiration that may have accumulated during the night. The
bag should be turned inside out and exposed to a moderate amount of sunlight
and plenty of moving air. Be sure to carefully tie or otherwise secure your bag
so that it does not blow away.
Your
bag's inital application of the DWR finish will gradually wear off, it is a
good idea to periodiocally reapply this finish. Inspect the seams under stress
for any separation or distortion in the weave.
Edited by John
Francis Maggio - Western Mountain Sports; Contributors: Roger Parry - Dupont
Dacron, Dr. Liz McCullough - Kansas State University, Greg Foweraker - Mountain
Equipment Co-op, Henry Heyburn - L.L. Bean, Amanda Lee - BHA, Peter Hickner -
Feathered Friends, Sheila Klien - Cascade Designs, Fred Dieter - Sierra
Designs, Eric Weidler - Sierra Designs.
Please send
your comments and suggestions, Attention John Francis, 1025 S. 5th St, San Jose
CA. 95112. Or fax to 408 287 8946.
http://www.orca.org/publications/bicsleep/index.html
COPYRIGHT 1999, ALL RIGHTS RESERVED