How To Make Your Winter Sleep System: Complete Guide

By Jake Reyes · October 7, 2016 · 9 min read

Tranquil winter scene of snow-covered trees in Megève, France amidst the Alps.

A winter sleep system is the whole stack between you and the cold: bag, cover, pad and the habits that keep them dry. Choosing the bag is the hardest part of that, and in winter it matters more than in any other season. Before you go out and buy the warmest sleeping bag you think you'll need, a few questions deserve an honest answer.

Questions to answer before you buy a winter bag

How important is weight? If you are trying to save ounces with a sleeping bag, you may make some sacrifices elsewhere, usually in warmth, durability or price. How warm do you like to sleep? Some people sleep better in the cold, others do not, and that preference should shape what you buy more than any number on a tag.

Then think about the environment. Will it be wet or dry? A bag that performs well in a dry, frozen climate can struggle in damp, heavy snow, and the reverse is also true. These are all questions to ask yourself before buying a sleeping bag for winter.

It also helps to remember that a bag is only one layer of the plan. Your clothing, your shelter and where you pitch it all change how cold you feel at night, so it is worth reading about choosing a winter campsite and how to keep your tent warm alongside this guide. If you want to compare specific bags once you know what you need, the roundup of the best winter camping sleeping bags is a sensible next stop.

Here are some sleeping bag features to look for.

How fill type changes warmth, weight and risk

How warm a sleeping bag will be depends on the thickness of the fill. That thickness, called loft, creates dead air space, trapping warm air next to your body. The thicker the fill, the more dead space there will be, and the less heat you lose to the night.

Down fill

The warmest winter sleeping bags per weight are made from goose down. Goose down provides 1/3 more insulation compared to high-tech synthetic fibers. This means you will get 1/3 more warmth for the same weight, or 1/3 less weight for the same warmth. Another benefit is that goose-down bags compress more than other bags, adding less bulk to your trip. If goose-down bags are maintained properly, they can last twice as long.

With all the benefits of goose down, there are some drawbacks to consider. Down absorbs moisture quickly. If the down gets wet, the loft collapses and will no longer retain heat. Moisture does not only come from the elements such as snow and rain but also from perspiration and respiration. This is an important reason to dry out your bag every day.

Storage matters too. Down keeps its loft best when it is not crushed for long stretches, which is one reason many campers prefer to stuff a sleeping bag in a loose sack on the trail and keep it lightly stored at home.

Synthetic fill

Synthetic sleeping bags, on the other hand, do much better when wet, making them better for wet and snowy environments. Synthetic bags dry quicker as well and usually cost about half the price of down. However, the disadvantage of synthetic bags is that they are heavier and bulkier.

My own view is that most beginners are better served by a synthetic bag in a damp climate than by a pricey down bag they are nervous about wetting. A cheaper bag you use confidently beats an expensive one you baby.

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Shape and size: getting a bag that fits

Shape

The best shape for a winter sleeping bag is a mummy bag. Mummy bags hug your body, making them the most efficient. These bags also come with an insulated hood that can be snugged closely around your head. Rectangle bags may be roomier, but they are bulkier, heavier, and colder compared to mummy bags.

To get the most out of your bag, look for one with a draft tube that lies against the full length of the zipper, keeping cold air out. Zippers are a natural weak point, since the stitching and the gap behind the teeth are where warm air escapes, so a good tube earns its weight. Mummy bags also often have insulated collars that wrap around your neck, keeping you even warmer.

Size

When looking for bags, make sure you get the proper-length bag. It should not be too large nor too small but fit you just right. If you get a bag that is too large, your body will have to generate extra heat to warm up the extra space, and small bags are never comfortable.

A good rule of thumb is, if you are 6 feet tall or shorter, a regular-length bag will do. If you are more than 6 feet tall, choose a long bag. If you get a bag that is too short, you risk stretching the bag, flattening the insulation, and making the bag colder. Pressed insulation is thin insulation, so any spot where your feet or shoulders push against the fabric becomes a cold spot.

Temperature ratings are a guide, not a promise

Temperature ratings can be helpful, but because there is no industry standard, different bags with the same temperature rating may feel different. A bag that is rated for 0 degrees may seem warmer or colder than another bag rated at 0 degrees from a different manufacturer. Treat the number as a rough way to sort bags into groups, then judge the details: loft, hood, collar and draft tube.

Another factor is that people have different metabolic rates. One person may feel comfortable in a 0-degree bag while another feels cold. What can you do knowing this? Buy a bag that is a little warmer than you think you need. Being too warm is easy to fix by opening the zipper, while being too cold at night is hard to fix at all, and in severe cases it can slide toward hypothermia.

You can also try sleeping in the backyard with various bags before you buy them. There are also some economic options, such as buying sleeping bag liners or adding a thin summer bag to fit inside a 3 season bag. Experiment and find out what you are most comfortable with. Eating something before bed and going to sleep in dry base layers will also help, and the guide to layering clothing covers what to wear.

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Sleeping bag covers and how to manage frost

Most winter sleeping bags are made with a shell material, but having a sleeping bag cover still has its benefits. Sleeping bag covers are waterproof yet breathable, keeping your bag from getting wet and protecting it from the elements. They are especially important if you plan on sleeping under the stars without a shelter. This extra layer will keep your bag dry from the outside, and make your bag warmer, as the cover will protect against the wind and add an extra layer of warmth.

There is one drawback to consider with sleeping bag covers. Normally, water that is expelled from your body passes through the sleeping bag insulation and sometimes condenses on the outside in the form of frost. With a sleeping bag cover, if you're not careful to brush this frost off every day, the moisture can work its way back into the bag.

The practical routine is simple. In the morning, shake or brush off the frost before it melts, open the bag up to air whenever the weather allows, and avoid breathing into the bag overnight. Even a few minutes of airing helps, and the same habit matters for any bag, since the sleeping bag is designed to hold warm air, which also means it holds your moisture.

Sleeping pads for your winter sleep system

Along with a good sleeping bag, another very important part of a winter sleep system should be a sleeping pad. A sleeping pad will not only make sleeping on the ground more comfortable, but it will prevent the ground from stealing valuable body heat. The reason is that the insulation under you gets squashed flat by your weight, so the bag beneath your body does very little work. The pad has to do that job instead.

There are 3 basic types of pads: open-cell air pads, closed-cell foam pads, and self-inflating pads.

Air pads

Air pads must be manually inflated, and offer decent cushion. These are ideal for saving space and backpacking. Some air pads are filled with down feathers to increase insulation. Pump bags are also available to help inflate the pads. Pump bags are manual pumps in the shape of a bag, saving you additional weight and space. They also keep your warm, moist breath out of the pad, which is a small but real advantage in freezing conditions.

Closed-cell foam pads

Closed-cell foam pads are light and inexpensive but can be more uncomfortable to sleep on. With a foam pad, you won't have to worry about air punctures, and they can also offer some extra cushion when sitting down. These pads also offer great insulation. They are decently durable too, and can take a beating without being ripped or torn.

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Self-inflating pads

Self-inflating pads are made from open-cell foam that expands in the presence of air. Because of this, they are able to take up less space when deflated, and self-inflate when needed, just like a sponge. Many people top them up with a few extra breaths or a pump once the foam has done most of the work.

R-value and stacking two pads

When choosing a sleeping pad, pay attention to the R-value. The R stands for resistance and means how resistant the pad is to heat transfer. The more resistant, the less heat transfer there will be between you and the ground. Compare R-values between pads rather than thickness alone, since a thick pad can still be a poor insulator.

When camping in cold weather, consider using two sleeping pads. One method is to use a high-R-value air pad or self-inflating pad on top of a closed-cell foam pad. The closed-cell foam pad will offer extra insulation and help protect the inflatable pad from punctures. It also gives you a backup if the inflatable pad fails in the middle of the night, which is a miserable time to find out.

Put together, the bag, cover and pads work as one winter sleep system, and weakness in any layer shows up as cold. If you are unsure where to spend, I'd put the money into the pad first, because ground cold is the one that sneaks up on people.