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Sleeping Bag Construction
Mummy bags are the most popular for backpacking and cold weather camping. They
are the most thermal efficient bags available. They are made to
fit close to the body by tapering down the legs. The taper cut allows
for less circulation of air. Low circulation creates dead air which
retains heat best. There is also a hood that covers the head, to
create a cocoon around the body trapping the valuable heat.
Rectangular Bags are best suited for warmer weather camping. These
bags are cut for comfort and not efficiency. Rectangular bags usually
do not have hoods, which makes it less desirable in cold weather.
Tremendous amounts of heat can be lost through the head. These bags,
because of their wider cut, have more circulation and less dead
air making them more difficult to heat.
Semi-rectangular bags are considered a sort of hybrid bag that
can be used in cool backpacking situations. They were presented
to the market as an alternative to mummy bags, because many packers
desired more room than mummies offer, while being lighter in weight
and more compactible than their rectangular brethren. To create
these bags different materials and means of construction are required.
There are two different types of insulation that exist today; down(natural
fiber) and synthetics(man-made material). Down is the most efficient
insulator on the market. Down is also the most durable. Some people
still use the same bag for over 10 years without losing any thermal
value. Down possesses the greatest amount of warmth to weight ratio.
It is the lightest and most compressible of all insulators. One
problem with down is that when wet, it only retains about 10% of
its thermal value and takes a very long time to dry out. Also, when
down is saturated it gains 128% of its weight. However, the shells
used by many of the manufacturers are very water resistent and breathe
well, making it more difficult to saturate the down.
There are three different types of down; 550, 650, 700 fill down.
The numbers mean how much water the down will hold per ounce of
down.(water is only a measuring tool, because it can be fully absorbed
by the down). 550 is the cheapest down available. It usually consists
of down and feathers. Feathers do not work as well as the down fibers.
650, until recently, is the best down available. 700 now is the
best down available. It consists of strictly down fibers and little
to no feathers. Because of the down/saturation problem, man has
been on a quest to create a more efficient, quicker drying, light,
and compressible alternative to down. Synthetics are usually cheaper
in price, but they are usually heavier, less compressible, and have
a shorter lifespan than their natural counterpart. However, Synthetics
dry quicker, absorb a small % of their weight when wet, and can
keep almost all of their thermal value when wet. So there appears
to be a compromise between the two. If you know that you will camping
in wet conditions it may be safer bet to go with a synthetic. If
that is no concern and neither is price, go with down. When choosing
a synthetic it is good to know the different types.
Hollofil II- A four-hole hollow polyester. This fiber is treated
with silicon to give it a softer hand and make it more supple. Hollofil
is the heaviest and bulkiest of all synthetics. However, usually
the cheapest. Great for car camping or sending boy scout on first(maybe
only) trip.
Polarguard- a longer continuous filament that is also made from
polyester. The continuous construction enables this synthetic to
be laid in any direction and aids the fill from shifting. This technique
creates an extremely durable bag by preventing tearing. Tears in
the filament can create cold spots, rendering the bag useless. Polarguard
is a mid-line synthetic good for the price conscious buyer and/or
beginner not willing to sacrifice any quality. Polarguard also has
a higher warmth to weight ratio than Hollofil. Polarguard comes
in two ways. Regular Polarguard and Polarguard HV. HV is the newer
filament that decreases weight and increases compressibility and
price. Because of the durability and price of this fiber, many manufacturers
experiment with this material and in 1996, many companies have started
to use Polargaurd 3-D, an even lighter version of the fiber.
Liteloft- a unique innovation in synthetics. The theory is taken
from the natural design of down. Tiny fibers are intertwined in
larger thick fibers that imitates down by boosting the loft of the
synthetic fiber. The result is the closest fill similar to down.
The most efficient of the synthetics, greatest warmth to weight
ratio, greater compressibility, and keeps its insulating value when
wet. Litelofts price is comparable to 550 down, but less expensive
than 650 and 700 fill down.
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