A topic I’ve heard debated many times is whether or not it is warmer to sleep naked in your sleeping bag during cold weather. Many hikers believe that it is.
Nearly all gear/technique issues are open to debate. Is a tarp better than a tent, shoes better than boots? There are good arguments on each side of most of these issues. There may be good arguments on each side of the “sleeping naked” issue, but there aren’t good FACTS on each side. : )
This topic came up on the AT last year when I saw a new outdoors magazine repeat the old tale that sleeping naked is better for staying warm. I was surprised when many folks in the shelter agreed, one even telling me that a military expert they knew told them it was true. That expert was dead wrong. I’m basing my opinions on experience camping in severe cold on, many, many nights; on high, cold mountains, and in the dead of the winter in Alaska, in temperatures as low as -55 F.
Most of the same principles for dressing for cold weather apply for sleeping in cold weather. Loose, layered insulation is the warmest. It is not warmest to be naked under your parka, just as it isn’t warmest to be naked in your bag. I like to wear just enough warm clothing to stay warm but still avoid sweating. If I’m chilled when I fall asleep, I may need to remove some clothes as I warm up during the night.
To sleep warm on those coldest nights on the AT or elsewhere, you’ll need a combination of a sufficiently warm bag and clothing. A balaclava is the most warmth per ounce that you can carry. Wear one on cold nights. Add as much additional clothing as you need. If it’s really cold, a carefully sealed water bottle filled with hot water, and wrapped in an extra item of clothing, will heat up your bag for hours.
Also, insulation from the ground is vital. A ground pad, preferably closed cell foam or a Thermarest style pad is best. Getting out of the wind and wet is also very important, of course.
Naturally, you want to avoid sweating, but if you’re sweating keeping warm is not your problem, keeping cool is. You SHOULD avoid sweating in your bag, so if you need to sleep naked to do so, you should. Otherwise, sleeping naked to stay warm is a big mistake, unless you have the right hiking partner, of course ; )
Colter