Staying Warm At Night In the Woods

This is part 2 of a multi-part series on backpacking equipment

  1. Portable Backcountry Shelters
  2. Staying Warm At Night In the Woods
  3. Fueling the Furnace
  4. Dressing Appropriately
  5. All the Other Stuff We Like To Pack
  6. And, Finally, What To Put It All In
  7. An Example Gear List

In part 1 of this series I spent some time talking about backcountry shelters which enable you to stay dry and bug free at night.  But that is really only half of the equation when it comes to spending the night out in the woods, unless you are camping in the tropics that is.  The other half is staying warm through the night.  Even in warmer climates the temperature will generally cool enough at night that some protection from the cold is desirable.  And in colder climates that protection is mandatory.

The Sleeping Bag
The most common means of staying warm at night is to cuddle down into a sleeping bag.  The sleeping bag provides a layer of insulation between you and the cold night air, keeping your body heat where it will do the most good.  There is an almost endless number of sleeping bags to choose from and walking into your neighborhood REI in search of a bag, without some idea of just what you want, can be daunting.  There are at least three significant factors to consider and several others that will impact the ability of a bag to keep you warm.

Each bag will have a temperature rating, a value assigned to the bag by the manufacturer, that is supposed to tell the buyer the lowest outside temperature at which you might expect to stay warm using that bag.  But because this is a manufacturer assigned value rather than an industry standard, and because some people sleep colder than others, this should just be used as a rough guide.  Take the time to look at reviews of bags you are interested in and see how those who have used the bag rate its temperature assessment.  Be sure that the bag you select will be warm enough for the conditions you expect to travel in.  You might find that you end up with at least two bags, one for warmer conditions and a second for when cooler temps are expected.


A second factor to consider when selecting a bag is its shape.  Rectangular bags are roomy and give an active sleeper room to thrash around at night.  Mummy bags taper down toward the foot, generally contouring around your body.  The widths and taper of mummy bags will vary by manufacturer.   The downsides to a rectangular bag include the extra space inside that your body needs to heat to stay comfortable, and the additional weight that comes from the extra material required.  The upside to the bag is its roominess for those who move around at night.  The advantages and disadvantages of the mummy style are generally the opposite of the rectangular bag.  The mummy bag will be easier to heat and keep warm and will not weigh as much in your pack.  And they work best for those who move little during the night, and especially for those who will spend the bulk of the night on their back.  But that is not an absolute.  I seldom sleep on my back when on the ground and toss and turn a lot.  Yet I use a relatively narrow mummy bag.  The reduced weight and superior heating are worth the inconvenience of moving around in the bag or, in my case, having the bag turn with me.

The final big consideration is the type of insulation used by the bag; either down or some type of synthetic material.  Currently down has a superior loft to weight ratio to any synthetic material, basically meaning you can stay warmer with less weigh in a down bag.  But down bags have two disadvantages.  One is the cost; high quality down costs more than the synthetics.  The other, potentially more significant disadvantage, is that if down gets wet it will clump and lose its ability to trap heat, and it dries very slowly.  Synthetic insulation, on the other hand, will still continue to provide significant insulation even when wet.

Other things to consider include draft collars and tubes, hoods, how it’s baffled, distribution of insulation around the bag, length of the zipper, the material used for the inner and outer shell of the bag, and your own comfort with it.  When I bought my last bag several years ago I went to REI with a list of potential candidates and actually tried out several of them.  The clerk would throw a bag up on the table and I would climb in, curl up, flip around, and generally try to get an idea of how well it fit.

Sleeping Pads
The insulation in sleeping bags generally works because it lofts up, trapping warm air between the fibers of the insulation.  But what happens when you lie on that insulation?  It flattens down and becomes nearly useless.  While we often think of the sleeping pad as something that makes the hard ground softer, its primary function is actually to provide a layer of insulation between you and the ground, taking the place of the flattened insulation in the sleeping bag.

There are three primary types of sleeping pads that are generally used in the backpacking community.  Closed cell foam is a cheap, lightweight alternative that many use.  Closed cell foam does not compress much and is usually rolled or folded to attach to your pack,  It is going to generally provide good insulation but not all that much in the way of making the ground softer.

Inflatable mattresses will generally provide the thickest, and thus softest, pad although they do have to be blown up every night when setting up camp.  Many of them will actually provide very little in the way of insulation so you should choose this pad carefully.

Self inflating pads are similar to an air mattress but with something like an open cell pad on the inside.  When the pad value is open the interior foam will expand, pulling air into the pad and inflating it.  When finished with the pad you will need to roll it up to push all of the air out of the pad and then close off the valve.  Self inflating pads are very common and come in a variety of shapes and sizes and are widely used.  They will have as much or more insulation as the closed cell pad and pack down smaller, although they will also be heavier.


I have used all three types of pads and have ended up with the Big Agnes Insulated Air Core pad as my go-to pad.  I have to blow it up in camp, but it is 2.5 inches thick and keeps the old hips and shoulders further away from the hard ground.  This pad packs down to just bigger than a quart Nalgene bottle and weighs about 1.5 pounds.

An alternative to the sleeping bag is to use a quilt.  This is similar to an unzipped sleeping bag that is used to provide a cover over and around you as you sleep.  The difference is that the quilt does not go below you.  Using a quilt is a recognition that the sleeping bag insulation below you is compressed and of little value, and thus can simply be left behind, reducing somewhat the weight of your covering insulation.  With the pad below and the quilt above you should be as toasty as if you were using a sleeping bag.

The downside to the quilt is that an active sleeper may find themselves frequently having to tuck under the edges of the quilt to avoid drafts during the night.  Many quilts actually have a footbox either sown into them or some method of forming one as needed.  This footbox helps to keep the quilt in position around your feet at night.

Your clothes can actually make a significant to your staying warm at night.  On trips where I anticipate colder evenings I bring a pair of lightweight down pants, coat and booties to wear around camp in the cool evenings and mornings as well as to supplement the bag or quilt that I am sleeping under.  Other clothes can be used as necessary to allow you to reach colder temperatures without having to buy a bag rated for the colder temp.

Pulling a large garbage bag or lightweight emergency bivy over your body, but inside your bag can also significantly increase your warmth by trapping the warm water vapor you perspire, even during a cold evening.  But be sure to put the bag/bivy inside your sleeping bag or quilt, otherwise all of the moisture will be absorbed into your insulation, reducing its effectiveness and increasing its weight.

Staying Warm in a Hammock
Hammocks present a different set of challenges to staying warm at night.  Being up off the ground, the wind has more of an opportunity to pull warmth away from your body.  The same measures you use on the ground to stay warm will work in a hammock but it is a bit more challenging.  Like those on the ground, hammock sleepers need to deal with both what covers them as well as what is underneath them.
There are many folks who use a sleeping bag in a hammock, although trying to manuver around inside of a closed sleeping bag in a hammock is a task that takes some getting used to.  I suspect most folks using a bag in a hammock will leave it unzipped and use it as a quilt to cover themselves with; I know I certainly did.  Alternatively you can just use a quilt, or top quilt, for this purpose.  The quilt will have a weight advantage over a bag since it does not have to be big enough to go completely around you.
Bottom warmth can be supplied by the same pad you might use on the ground, and many people do just that.  I have found it to be a challenge to keep the pad below me though.  Seems like it wants to be on top instead.  I believe the pad will work best for those who are relatively inactive sleepers, or those whose hammocks have a built-in pad pocket or dual layered bottom.  The alternative to the pad is to hang a quilt, or bottom quilt, underneath the hammock, pulled up tight enough to stop air flow between the hammock and quilt, but not tight enough to compress the quilt insulation.  I really find that laying in a hammock nestled between two quilts is very comfortable.  The downside to the bottom quilt is that it is heavier than a pad so those really concerned with weight will either use a pad or a shorter quilt that will cover the torso and use a pad under the legs.

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