Sleeping Warm

It was cold. I had a 0 degree sleeping bag but felt chilled. I pulled my down jacket into the sleeping bag and laid it over me for extra insulation. There were seven of us packed into a lean-to so tight that one person couldn’t move without affecting others. With insulating bodies on either side of me and the down jacket supplementing my sleeping bag I slept warm for the remainder of the night despite plummeting temperatures that made everyone begin snoring. I can’t claim that I didn’t join the chorus at some point.

Staying warm at night while you are winter camping is crucial to a successful trip. Having a “winter-grade” sleeping bag, or using two sleeping bags, is an easy and obvious first step. However, there are many other actions one can employ to ensure a good night’s sleep.

This chapter covers the components of a winter camping sleeping system, preparation steps before sleeping, using external heat sources, dressing for sleep, personal variations, adjustments during the night and how to handle the morning after.

1.1     Components Of A Sleeping System

A sleeping system to keep one warm overnight includes several components: a sleeping pad(s), a sleeping bag, sleeping bag liner and possibly a bivy bag or overbag.

1.1.1        Sleeping pads

A good sleeping pad is a crucial element to staying warm at night. What is under you is more important in keeping you warm than what is on top of you. Unless you have the right amount of insulation below you the ground will absorb most of the radiant heat vented by your sleeping bag and you’ll feel cold at night. You can prevent this by using an insulated sleeping pad. This compensates for the fact that you are lying on your sleeping bag, compressing the fill, eliminating most of its loft and heat retention capabilities.

Pads are rated by R-value, the measurement of insulation, ranging between 1.0 and 8.0. The higher the R-value, the better it insulates. A closed-cell foam pad is a thin, dense foam made of closed-air cells that block water and stop air circulation. Self-inflating pads are a combination of open- and closed-cell foam. Open-cell foam pads have open-air cells that absorb air and create more cushioning. Inflatable pads provide superior comfort but you can get cold spots where hips or shoulders compress the pad. Closed cell pad provide superior insulation but don’t provide much cushion.

Another alternative is to use a down filled sleeping pad such as Exped’s Downmat 9 which has an R-value of about seven. A Downmat more than equals two regular pads-a self-inflating and a closed-cell pairing-in insulation. While I’ve never used a down-filled pad, I am told they are very comfortable. Weight-wise a Downmat 9 weighs two pounds, while the two Therm-a-Rest pads will end up at three pounds six ounces.

Typically I use a combination of a closed-cell pad and an inflatable Therm-a-Rest pad. The closed cell pad has a R-value of about 2.6 and the Therm-a-Rest has an R-value of about 3 for a total of 5.6.

I recently discovered the combination of using an inflatable pad on the bottom and a closed cell pad on top for winter camping. It seems a bit counter-intuitive to use the inflatable on the bottom but it provides a cushion and floats the closed cell pad off of the cold snow. This counter-intuitive stacking of the two is worth trying if you are going to be spending a lot of time sleeping in the snow.

Closed cell sleeping padThermarest   Sleeping Pad adjustments

Many campers over-inflate their sleeping pads making it too hard and increasing the likelihood of sliding off the pad. To properly inflate you pad try this process: Inflate the pad fully, then lie on the pad and lean on the pad pressing down with your elbow. Let out enough air so that your elbow makes contact with the ground, then close valve.

If your pad is too slippery you can give it some texture by washing the surface of your pad with soap and water and let it dry thoroughly. Then use silicone caulking or SeamGrip to make a pattern of dots along the surface of the pad. Most of your pattern should reside on the main torso / hip area. After drying for 24 hours your slip-free pad is ready to use.

1.1.2        Sleeping bag

If you want to be comfortable winter camping you need more than a summer or three season bag. When the temperatures dip down to zero you need a mummy bag. Mummy bags taper from head to foot, creating a smaller-volume bag that makes it easier to maintain body heat. Additionally mummy bags have a hood you can draw around your head for extra warmth.   Sleeping Bag Terminology

Even a simple piece of gear like a sleeping bag can have a confusing number of parts, features, and terms. Here are the basic parts of a typical mummy bag.[1]

Sleeping bag parts

Baffles: The internal pockets of insulation that prevent the insulation, from shifting, clumping, and developing cold spots. Sewn (or stitch) through and box are examples of baffle techniques.

Layers: Construction method using two offset layers of synthetic insulation. The top layer is sewn to the shell and the bottom layer to the lining.

Shingles: Construction method using overlapping sheets or pieces of insulation stitched to the bag’s shell and lining. Typically used with synthetic insulation.

Shell: The exterior shell keeps the insulation close to your body, and provides a little insulation on its own. Some shells are made of water-resistant materials and some with waterproof-breathable membranes.

Lining: Usually made of a softer material than the external shell, the interior lining is designed to feel soft and wick moisture away.

Hood: An insulated hood prevents heat loss from your head, and keeps warm air from escaping the rest of the bag.

Pillow Pocket: Give you space to stuff extra clothes or a camp pillow.

Hood, Chest, or Stash Pockets: A small pocket in the hood for your watch or MP3 player.

Draft Collar: An insulated collar, tightened by a cinch cord near your neck and shoulders, intended to prevent heat from escaping and cold air from entering.

Draft Tube: A thick tube of insulation along the zipper that prevents air exchange.

Zippers: Come in different lengths. A full-length zipper can help regulate your temperature if you start to sweat while a half-length zipper may save some weight. Zippers should be anti-snag. Many bags give you a choice between a left- or right-side zipper. A right- and a left-zippered bag with compatible zippers may be zipped together.

Zipper Pulls: Winter bags often feature long cords on the zippers, for easier use with gloves. Some bags have glow-in-the-dark zipper pulls for easier nocturnal exits.

Pad Loops: Connect your sleeping bag to your sleeping pad, holding the pad in place and preventing the bag from sliding off the pad.

Foot Box: The space at the foot of the bag. Some bags offer venting from the foot box. In winter, extra space in the foot box can be used to store hot water bottles, extra clothing, and boots or boot liners.

Hang Loops: Permit the bag to be hung to dry to maintain its loft.   Temperature Range

Consider the temperature range you require. You should consider whether you sleep warm or cold and take that into consideration when buying your bag. The temperature rating really means you it will keep you alive at that temperature–it does not mean you will be warm; so add 10-15 degrees F to achieve a level of comfort. Thus, a 0 degree-rated sleeping bag should keep you relatively warm into the teens, provided you’re on an insulated sleeping pad, wearing a base layer and hat. The excess insulation may weigh more, but you will appreciate the extra insurance.

Temperature ratings cited by sleeping bag manufacturers can vary widely and may be estimated from the fill, features, and sizing. Your best defense is to select bags from proven, quality manufacturers whose temperature ratings have been validated by the community at large. Different brands and different designs run warm or cold talk so talk to friends and research the internet. Feather Friends and Western Mountaineering make well regarded down sleeping bags.   Sleeping Bag Insulation

Your sleeping bag choice requires a decision between down and synthetic insulation. Down insulation weighs less, lasts longer, compresses smaller, and costs more. Down bags with a fill power rating of 800 or higher are significantly lighter and more compressible than bags with lower fill power rating ratings such as 650. They are also much more expensive. Down is more durable than synthetic insulation when compressed frequently. High fill power down bags can retain their resiliency and loft for 15-20 years while synthetic fills break down with five or six years of use. My first quality down bag lasted 30 years with moderate use. Synthetic sleeping bags dry quicker, provide better insulation when wet, and cost less.   Sizing your sleeping bag

Make sure your sleeping bag is the right size for you. If there’s too much girth and extra space your body will lose heat trying to warm that empty space. However, you might want extra length to your sleeping bag to sleep with boots, water bottles, cameras, clothes, etc. to keep them from freezing. Consider using a bag specifically sized for men or women as girth specifications change between models.

If you don’t have a really warm winter bag, consider an insulated over-bag that you can use with your three-season one to boost the temperature rating or bring two sleeping bags.

1.1.3        Sleeping bag liner

A sleeping bag liner serves as an insulating layer inside a sleeping bag, it provides a layer of protection between your body and any water bottles or clothes you include in your sleeping bag at night and they keep your sleeping bag clean from dirt and body oils. A sleeping bag liner might consist of a fleece blanket, silk mummy bag or a vapor barrier bag. My experience is that blankets tend to get tangled so look for something shaped like your sleeping bag.

I routinely use a silk sleeping bag liner inside all my sleeping bags for both comfort and warmth.

  • A sleeping bag liner adds warmth. It can add several degrees of warmth to your bag depending on the fabric, which allows one to buy a lighter bag but still get the temperature rating of a heavier bag.
  • For individuals with old sleeping bags with compressed insulation that has lost warmth, a liner allows a boost to the warmth and delay the purchase of a new bag.
  • A liner can act as a draft barrier keeping users warmer and can fill up the excess room in a mummy or rectangular bag, boosting warmth.
  • A liner keeps a sleeping bag clean and minimizes the need for laundering. Washing a liner after a trip is way easier (and cheaper) than going to a Laundromat and washing a whole sleeping bag in a large commercial machine. Washing a sleeping bag is the fastest way to ruin it. Most manufacturers recommend using a liner and just spot-cleaning the sleeping bag.
  • A liner adds comfort. A liner made of Silk or CoolMax is more comfortable against the skin than the linings of many bags.
  • Many liners will help wick away moisture, keeping users drier to help them sleep more comfortably. And a liner helps avoid the initial shock of climbing into a cold sleeping bag.

I have used a Design Salt silk sleeping bag liner for many years. I have used this liner in a variety of weather conditions with temperatures ranging from -teens to mid-70s. The silk liner is lightweight – it only weighs 4.7 ounces. The liner adds 9.5 degrees of warmth to my sleeping system. It is breathable, wicks moisture away from skin and is soft and comfortable to the skin. Finally it is the ideal size. I am 6′4″ and found the sizing of liner to be ideal. The 95″ long bag features a drawstring hood, a 35″ wide opening taping to a comfortable 22″ boxed foot end.   Vapor Barrier

A vapor barrier is a special class of sleeping bag liner. A vapor barrier is made of a waterproof, non-breathable coated material and the concept is to keep a sleeping bag dry on multi-day trips by preventing body perspiration from getting trapped in the insulation of the sleeping bag. In ideal dry conditions the heat generated by the body drives the moisture through the insulation. However, in extreme cold this moisture might become trapped in the insulation and freeze. By using a vapor barrier the moisture is contained and can be removed by turning the vapor barrier inside out and shaking off the flakes as the moisture freezes. Used properly, a vapor barrier liner can allow you to sleep comfortably in temperatures 10 or 15 degrees lower than you could without a liner; used improperly, a vapor barrier liner leaves you sleeping covered in your own sweat.

1.1.4        Bivy Bags and Overbags

Bivy sack is short for “bivouac sack.” Bivy bags originated as lightweight emergency weather protection for sleeping bags. Bivy sacks have evolved into bivy shelters which may include mesh panels attached to the head opening, plus small suspension systems (poles, hoops or stiffened wires) that lift the bivy off a camper’s face.

A basic bivy keeps a sleeping bag clean and dry. A bivy can hold a sleeping pad in place and may increase warming capacity by up to 10 degrees. It is the increased protection and warmth that is worth consideration depending upon the type of winter camping shelter (e.g. snow shelters or floorless tents) employed.

An overbag is a generously sized liner or sleeping bag cover that fits over your sleeping bag to provide extra warm and protection. Overbags operate similar to bivy bags but lack a hood. One approach is to borrow a summer-weight bag and use that as an overbag

A major factor in choosing a bivy or overbag is breathability. Condensation from moisture escaping your body through your sleeping bag will reduce the performance of your sleeping bag.

The disadvantage of using bivy/overbags is that they provide another layer to exit / enter during the night and additional weight to pack.

1.2     Preparation Before Sleep

Before turning in to sleep you can increase your comfort level by simple preparation of your sleeping system and your body.

1.2.1        Preparing your sleeping system

As soon as you set up your site you should set up your sleeping system. If you are using a self-inflated air mattress let it self-inflate and then add puffs of air right before bedtime. You don’t have to worry about moisture buildup even in winter; freezing of moisture in the pad isn’t an issue unless you are doing this daily for months at a time.

Fluff your sleeping bag up very well. This will allow more time for the sleeping bag to regain its loft. Also, you should give your sleeping bag a good fluff just before getting in it. This also helps the bag retain loft throughout the night.

Put tomorrow’s clothes under your sleeping bag. If you put tomorrow’s clothes between your sleeping pad and your sleeping bag, your clothes will be warm when you go to put them on the next day. The additional layer between you and the ground will also help you keep warm.

1.2.2        Preparing your body

During the winter it’s important to be adequately hydrated. Your body demands more water in the winter as your lungs lose moisture humidifying and warming the dry, cold winter air. The average person may require 2-4 liters/quarts per day during winter exertions before sleeping. In order to burn fuel efficiently you must keep your body hydrated.

Avoid caffeine, alcohol and nicotine. Caffeine is a diuretic which causes water loss increasing dehydration. Although alcohol has some caloric value, it is a detriment in cold weather. Physiologically, alcohol creates peripheral vessel dilation which results in the rapid loss of body heat. Nicotine is a strong vasoconstrictor that decreases circulation to your extremities and promotes frostbite.

Eat a hot, hearty meal for dinner. Your body will use this fuel to keep you warm throughout the night. If the weather is really bad and you don’t feel like cooking a big meal, then cook the meal that is easiest and fastest to make. When cold-weather camping, carry a freeze dried meal to provide a quick, easy hot meal.

Eating a high calorie, high fat content snack before bedtime will give your body more fuel to help keep you warm. Proteins, such as cheese, nuts, or grains, are better than simple sugars. Proteins release their energy more slowly than sugars, keeping you warmer through the night.

Do calisthenics to get your circulation moving and your metabolism going. Take a brief hike around camp, or do jumping jacks or pushups to increase your metabolism and get warm before getting into the sleeping bag.

Go to the bathroom before bed and save yourself a middle of the night trip in the cold.

1.3     External Heat Sources

An external heat source such as a hot water bottle, sleeping companions, warm rocks or chemical packs, will bolster your own body heat. Fill a leak-proof water bottle with hot water. Wrap it in a spare fleece layer or sock, place it in your sleeping bag and sleep with it. You can even pre-warm your sleeping bag with the hot water bottle before you slide into it to.

Depending on your tent mate you can snuggle next to one another to share warmth. By keeping sleeping bags close together in the tent you can take advantage of your partner’s heat.

Take heated rocks from around the campfire and place them inside your cooking pot for a safe heat source inside your tent.

Chemical heating packs work great for hands and feet. Layer them between socks or gloves – never put them directly next to your skin. Chemical heat packs usually last several hours.

What to do if you are in your bag and wearing everything you have, but you’re still cold? If you have an external heat source (e.g. hot water bottle or chemical heating pack) put them between your legs against your femoral artery. This warms your blood directly and quickly increases body temperature.

1.4     Dressing For Sleep

Change into clean, dry, loose fitting clothes prior to climbing into your sleeping bag. Wear wool, silk or polypropylene long underwear tops and bottoms. A hat, balaclava or hood will help keep your head warm. Accessories such as socks, light gloves/mittens, and a scarf around your neck will also help retain body heat.

Perspiration in the clothes you wore during the day will chill you at night. As your body warmth evaporates this moisture it gets trapped in the insulation of the sleeping bag, reducing its effectiveness.

Make sure your feet are as dry as possible before going to bed. Wear dry sleeping socks or booties or you can “dry” wash your feet with a good foot powder that contains aluminum chlorohydrate, to dry the skin and reduce perspiration.

If you wear too much to bed you can risk compressing your sleeping bag insulation and you risk getting overheated. You want to avoid sweating during the night. If you feel constricted in your bag, you have got too many layers on.

Keep a jacket or vest handy to utilize for adjustments during the night.

1.5     Personal Variations

Some people have ‘must be warm’ spots on their bodies. For some people it is their head or feet. Mine is the small of my back. If my lower back is warm, I feel warm and can tolerate other parts being chilled. Bring an insulating layer (down jacket or fleece) into your sleeping bag to place around your cold sensitive areas. If your feet are cold, wrapping them in a fleece jacket may do the trick for you.

1.6     Adjustments During The Night

Don’t bring wet clothes or boots into your sleeping bag as moisture will travel from wet clothes to sleeping bag. If you must bring leather boots into your sleeping to prevent them from freezing consider putting them in a stuff sack and placed into the foot of the sleeping bag. You can also put the boots in a sack and place them under your legs between your sleeping bag and the pad underneath.

Make certain to sleep with your face outside of your sleeping bag. Your breath contains a great deal of moisture that can cause dampness to collect in the bag as you sleep.

Avoid overheating at night. Being too warm produces perspiration, so vent your bag if needed or take off your hat.

If you are cold add more insulation by using your jacket as an additional layer and seal the area around your neck by cinching your mummy bag or use extra clothing to seal off the opening around your neck. I have found putting a down jacket loosely over me to be more comfortable than wearing the jacket and it prevents sweaty arm pits.

Keep a snack available for the middle of the night, so if you do wake up cold you can replenish lost calories and warm back up again. Semi-sweet chocolate bars or trail mix work fine. One of my early winter camping experiences was during college when my high school biology teacher and I went camping in the Catskill Mountains in late November. It snowed and the temperature dropped during the night. Typical of almost every winter camping experience I had, we had gone to sleep early in the evening. However, this evening I woke up shivering and cold. I was certain it must be the dead of night and I was hopeful that day break wouldn’t be too far off. I shone a light on my watch, revealing it was only 9:22pm! I feared it was going to be a long, long, cold night. Fortunately I had brought some chocolate and raisins. After a quick snack I pulled my extra clothes into the sleeping bag filling the space around my shoulders. I then managed to sleep through the night.

If you have tried all these measures and are still very cold, don’t be afraid to wake someone!


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