How To Sleep Warmly

Lucky is the warm sleeper. You know you’re a part of this club if you’ve ever slept blissfully through the night with the zipper to your bag hanging open while companions with nearly identical sleeping bags complained of the bone shivering cold.

Warm sleepers and cold sleepers are born that way, due in large part to metabolism & body size. But a whole bunch of other factors comes into play that influences your ability to sleep comfortably through the night, such as how much water and food you consumed that day and how much insulation lies between you and the heat-sucking ground.

Hit the sack with a hat, but try not to overdress.
Hit the sack with a hat, but
try not to overdress.
So, cold sleepers, don’t despair. You can level the playing field with a few easy-to-follow tips to help you generate and conserve more body heat when the night turns frosty. Here’s how:
1. Get enough”bag” for your buck. Select any temperature rating for your sleeping bag that’s adequate for the nighttime temperatures you’re likely to encounter. Head into New Hampshire’s the White Mountains in November with a 35-degree bag, for example, and you’ll likely be a cold pup. For a more in-depth discussion on temperature ratings, see “Degrees of Comfort.”

2. Hold onto your heat. A sleeping bag’s pattern plays a big role in your ability to retain body heat. If you’re a serious camper or backpacker, your slam-dunk choice is a mummy-cut bag for the simple reason that there’s less space inside that needs to be heated and the close-fitting hood prevents heat from leaving. (Attention women: new women’s packs conform to the realities of the female form and metabolism — narrower fitting in the shoulders, wider in the hips, shorter overall, and extra insulation in the foot area — to create a bag that’s easier to heat up.)

Other warmth-enhancing bag highlights to look for: an insulated draft collar, which drapes or cinches around your neck similar a gasket to seal in heat; a hood with loads of padding as well as cinch cords to narrow the face hole; and an insulated zipper draft tube running the entire length of the zipper.

3. Get off the ground. The area is always colder than you, so without an insulating layer between you and it, you’ll be robbed of precious body heat. Your best bets in pads are either the closed-cell foam variety or self-inflaters. See “All About Backcountry Beds” for more about the buying considerations that go into selecting a pad. Tip: When camping on snow or frozen area, the best method for warmth is to carry two pads, a smooth, full-length covered-cell foam pad topped with a full-length self-inflater.

4. Eat before you sleep. Think of your body as a furnace that needs stoking including food to generate heat. Treat yourself to some high-calorie indulgences before turning in. For quick heat, carbohydrates like a cereal bar will rev your internal motor almost instantly, but the burn peters out after a few hours. That’s where proteins and fats come in. Peanuts and beef jerky, for example, are like big ol’ Yule logs that burn long and slowly to help generate metabolic heat into the wee hours.

Special Considerations

Women: bring some tampons even if you aren’t expecting to need them; backpacking package do weird things to your cycle.

5. Drink your fill. Blood is to your figure what water is to a hot-water heating system in a house. Run low on fluid & your blood pressure begins to drop as the volume of blood decreases. Another side effect is that blood viscosity increases & flow becomes sluggish, which slows its progress throughout small capillaries in your extremities. The whole total is you’ll begin to sense cold. Get in the habit of drinking beverages even before you feel thirsty throughout the day & hydrate in a big way at dinner time. Tip: Cold water creates a personal net energy loss, so drink hot beverages before bedtime.
6. Zip into a tent. A tent creates a buffered airspace around you to counteract heat damage on calm, cold nights as well as windy nights. Maximize your tent’s warmth potential by pitching camp sheltered from prevailing winds, & try to stay out of depressions or hollows where cold air settles. To ward-off time chill, scout out a tent location that will get full sunlight at daybreak. Tip: four-season campers should think to purchase a convertible tent with zip in-zip out panels that cover breezy mesh panels to retain precious body heat. A well-designed tent can be 5 to 10 degrees warmer than the outside temperature.

7. Wear the right amount of clothing. Too much bulky clothing can strangle blood flow & needlessly compress the bag’s insulation. Use non-constricting synthetic long underwear; preferably, a pair that’s not wet from the day’s activities. Vital to staying heated: cover your noggin with a synthetic or fur pullover hat. Tip: Reduce the amount of internal air space that needs to be warmed in a bag by loosely stuffing next day morning’s clothes around your feet or along your sides. As a bonus, you’ll wake up to prewarmed clothing.

8. Give your bag a boost. Slip your bag into an overbag & you’ll ratchet up the comfort factor a good 10 to 20 degrees. Another warmth booster that also happens to preserve your bag’s interior is a liner, which can add about 10 degrees of warmth. In a compression, try draping a down parka, a shell coat or any apparel item over your bag to add a few precious degrees of heat.

9. Get your blood pumping. Remember as a kid when you warmed your h&s by swinging your arms like a windmill? That’s outward force powering blood into your extremities, & it works. So does a brisk jog-in-place, or anything that temporarily elevates the heart rate. As simple as it sounds, brief exercise before bedding down will turn your body into a blast furnace that quickly changes a crinkly, cold nylon bag into a cozy cocoon.

Conversely, once inside the bag try to prevent your movement to a minimum. Thrashing & rolling creates a bellows effect that blows hard-earned warmth right out the neck opening of the bag.

10. Maintain loft. Trapped air is at the core of a sleeping bag’s ability to retain your body heat, so it figures that the more fluffed up & “lofty” the bag, the greater its heat conserving ability. When you arrive in camp, present your sleeping bag as soon as possible & grab one end & give it a few good fluffing shakes. At home, avoid keeping a bag compressed too much or too long. Synthetic fills are more easily damaged in this way than down. Worse still is leaving a stuffed synthetic bag to overheat in the trunk of your car. See “Lofty Thinking” for more storage advice

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