Usage (Summer vs Spring/Fall vs Winter vs Mountaineering)
- Temperature ratings are imprecise: It is best to take
the temperature ratings assigned by manufacturers as a rough guide.
There is no industry standard method of determining temperature
ratings of sleeping bags. While you can assume that one manufacturer's
20o F sleeping bag will keep you warmer than
that same manufacturer's 30o F sleeping bag,
you cannot assume that one manufacturer's 20o
F sleeping bag will keep you warmer than another manufacturer's 30o
F sleeping bag.
- People and situations vary: We all have different metabolisms
and degrees of cold tolerance. Two people can be side by side
in identical sleeping bags while one is "a bit too warm" and the other
is "freezing." Multiple factors can affect how warm a person feels
while they sleep: amount and type of clothing; sleeping pad insulating
capacity; tent insulation and vetilation; type, quantity and warmth
of food/liquids recently consumed; level of exertion during the day;
wind; humidity; etc.
- Consider a temperature range: Given the imprecision
of manufacturers' ratings and given the wide variation in people's comfort
levels, it is advisable to consider bags within a range of temperature
ratings. Moontrail has divided sleeping bags into the following
four classes based on manufacturers' ratings and bag design:
- Summer camping: 40o to 50o
F (4o to 10o
- Spring/Fall camping: 15o to
35o F (-9o to
- Winter: -5o to 10o
F (-20 to -12o C)
- Mountaineering: -40o to -10o
F (-40o to -23o
- Mummy: Very space and weight efficient because their tapered
shape reduces the amount of fabric and fill that must be packed and
carried. The lack of dead space allows these sleeping bags to
warm up more quickly and keep you warmer in colder temperatures than
does a bag with a less tapered cut. Some people find the cocoon-like
feel comforting, others find it claustrophobic.
- Rectangular: The whole point of a sleeping bag is to let you
sleep comfortably. If a mummy is too constraining, a few more
ounces of carrying weight and a few more cubic inches of sacrificed
pack space is a reasonable price to pay for a good night's sleep. Rectangular
bags also lend themselves to a wider range of uses: extra bed padding
in a cheap hotel room, a quilt at home, a guest bed for your hardier
friends. However, because rectangular bags are more difficult
to warm up and bulkier, they are best suited for summer camping and
- Semi-rectangular: A cross between a mummy and a rectangular
bag. You could say "the best of both worlds" or "the worst of
both worlds" (no compromise is perfect). A semi-rectangular sleeping
bag sacrifices some thermal efficiency and pack size for extra wiggle
room. Though some mummies are designed so they can be coupled,
semi-rectangular bags often provide a more natural fit when two people
wish to zip their bags together and share body heat.
Fill (insulation material)
- Performance: Down provides the best insulation for weight
and volume (ie, it is light and packs small). However, down is
a very poor insulator if it gets wet and down is relatively expensive.
Polarguard 3D, Primaloft and Thermolite are all high-end symthetic
fills. The fiber manufacturers each claim benefits for their particular
formulation. Published studies by disinterested parties using
objective tests are lacking (if you know of any valid studies comparing
the various fills, please let us know).
Primaloft is known
especially for its ability to retain insulating capabilities when wet.
- Price: As you would expect, the higher performing fills are
more expensive. If you don't mind a slight weight and volume
penalty, bags using less expensive fills can be a bargain for camping
or backpacking in mild-to-moderate weather.
- Fill Ratings: The rating a down bag is given describes
the lofting capabilities of the down used. The number is the amount
of volume one ounce of down will fill in cubic inches. For example:
a bag with down rated at 600 will fill 600 cubic inches, while one with
800 rated down will fill 800 cubic inches.
A higher fill rated bag will generally retain it's loft longer than
one with a lower fill rating. In addition, a higher fill rated
bag will compress more and be lighter than a lower rated fill bag in
the same temperature category.
- Length: The lengths listed in the tables are from the bottom
of the bag to the top of the "body" portion of the sleeping bag (ie,
the hood is excluded from the measure). Measure your height when
standing from the floor to your chin, plus give yourself a couple extra
inches of space (if your feet are pressed against the bottom of the
sleeping bag, it could be difficult to keep them warm during the night).
If you will be placing a few items (eg, the next day's clothes,
water bottle, camera) at the foot of the sleeping bag, add a few more
inches to your toe-to-chin height. There is no point in buy a
bag much longer than your toe-to-chin height because the extra space
just increases weight, pack-space and cost while requiring you to warm
a larger amount of dead space in your bag.
- Width: If you do not mind a tight fit, you can save weight
and pack-space with a relatively narrow bag. Because narrower
bags require less fill, they are often less expensive than a comparable,
- Hood: As much as 25% of a person's body heat is lost through
the top of the head. Insulated hoods are a standard feature on
most sleeping bags (except summer bags). Often tightened with
a draw string.
- Multi-sectioned hood: Hoods fashioned from multiple panels
provide a better fit than single panel hoods.
- Velcro closure tab: Often found at top of zippers and on draft
collars to ensure that the zipper or collar does not open when you move
around in the sleeping bag.
- Insulated draft collar: Helps keep the warm air in and the
cold air out by forming a collar around your neck - often tightened
with a drawstring.
- Staggered seams: Help prevent cold spot by ensuring that seams
of the inner liner do not line up with seams on the outer liner.
- Zipper draft tube: Runs the length of the sleeping bag inside
the zipper. Keeps cold air from seeping in through the zipper
Care of the sleeping bag
- Storage sacks: Do not leave your sleeping bag in its
stuff sack for long periods of time. Sleeping bags can loose their
loft and their insulating abilities if maintained in a compressed state
for too long. It is best to store a sleeping bag in a large, breathable
- Bag liners: A bag liner helps keep your sleeping bag clean
by absorbing your perspiration and the grit from the previous day's
hike. A clean sleeping bag is warmer (oils don't make good insulators)
Tips for staying warm
- Stay dry: If wet, dry yourself off before getting into the
bag. In the sleeping bag, adjust the hood tightness and zipper
height to prevent sweating. Do not breath into the sleeping bag
which causes condensation within the bag. The insulation value
of all fills decreases when they are wet.
- Use a sleeping pad: A pad not only increases your comfort,
but provides an important layer of insulation between you and the heat
- Wear long underwear: Long underwear keeps you warmer by retaining
heat near your body, keeps your sleeping bag drier, and helps keep your
- Wear a hat: Even if your sleeping bag has a hood, a hat provides
a layer of insulation next to your skin that retains heat.
- Eat and drink well: Your body needs plenty of calories and
fluids to maintain a warm state in a cold environment.
- Loft the bag: Lay the sleeping bag out at least an hour before
bedtime. This allows the insulation to expand which maximizes
its insulating ability.