2. Secure Your Campsite and Flatten Your Sleeping Surface
Once you’ve secured a location that’s reasonably dry, flat, and protected from the elements, set up your tent. If conditions allow, clear away any snow to expose the dirt and flatten the site with your tools or boots. Climb into your tent, and use your knees to smooth out the ground area were you’ll be sleeping. “Don’t wait until later to do this,” says polar explorer and all-around cold expert Eric Larsen. “Once the snow melts and refreezes, it’s hard to manipulate. I also create a shallow trough for myself so I don’t roll around.” This shaping technique helps to reduce ambient space and potential heat loss from cold exposure, which could make for a miserable night or subject an individual to the early stages of hypothermia or frostbite.
How Does Your Body Lose Heat?
- Evaporation: Evaporation causes a cooling effect. The body loses 85% of its heat through sweating during intense exercise. Wet clothes from sweating and increased respiration also trigger a drop in body heat.
- Radiation: Radiation causes heat to move away from the body. The body may lose more than 50% of its heat from radiation at temperatures lower than 68°F (20°C).
- Conduction: Conduction is the transfer of heat from physical contact. Conduction occurs at 68°F (20°C) and is responsible for the loss of body heat from sleeping on the cold ground.
- Convection: Convection occurs when a heated fluid (liquid or gas) travels away from a source. Take the example of a hot cup of tea. The rising steam coming off of the cup indicates the movement of heat as hot water transitions into gaseous water (wet steam).
3. Bring an Insulated, Closed-Cell Foam Sleeping Pad
Conduction is the culprit for the heat loss that occurs when sleeping on the cold ground, and even a “warm” cold-weather sleeping bag is a cold bag without a quality, insulated pad underneath it. Most self-inflating air mattresses only insulate down to about 30°F, so if you want yours for comfort, lay down a closed-cell foam pad (or CCF) first, like the Therm-a-Rest Ridgerest SOLite Solar (Figure A). This aluminized, coated pad is highly durable and has a lightweight build—we’re talking under 19 oz—and its R-3.5 rating (detailed below) is sure to keep you insulated. Simply throw your self-inflating mattress on top. Some backcountry experts even recommend layering the CCF pad on top of your air mattress.
Sleeping Pad Ratings: What Is an R-Value?
An R-value refers to to the ability of an insulated material to resist the conductive flow of heat. The higher the R-value rating, the more effective a sleeping pad is at thermal insulation. As always, field testing is the only tried-and-true method when it comes to backcountry gear. Factor in critical features such as a sleeping pad’s weight, compressibility, and comfort before making your purchase.