When it comes to polite conversation, stay away from topics such as politics, religion, and whether or not to layer up in a sleeping bag.
Over that final topic, I’ve seen disputes break out in bars, on message boards, and riverbanks. The primary point of contention is how much clothing you should wear beneath your sleeping bag. Some argue that sleeping in as little clothing as possible will keep you warmer (with more than a few staunch advocates for sleeping entirely in the buff). Others think it’s ludicrous to keep warm if you don’t use your existing jackets, jeans, and base layers.
Both sides have compelling arguments. Your outdoor experience and the time of year you usually camp will ultimately determine your preference. To understand the nitty-gritty specifics of the argument, I turned to numerous specialists with various backgrounds in textiles, sleeping bag manufacture, and real-world traveling.
So do two sleeping bags keep you warmer? Yes, sleeping in a bag with 10 CLOs will keep you “warm” at -46.12 F. As long as you ignore the air gap between the bags (which will provide additional insulation) and any compression of the insulation (which will reduce insulation), then you can just double the bags and add the CLOs (just like with clothing).
The Dress-Downers are a group of people who dress up for special occasions.
“I have a strong personal opinion on the matter. You always wake up sweating, which makes you chilly [because of the cooling effect of your sweat on your skin], and you can’t get out of it.” “Come in chilly and let the sleeping bag do the work,” Karen Beattie, Polartec’s product manager, advises. “I’ve learned over the years that crawling in wearing a jacket and falling asleep like that is the worst mistake I could do.”
Beattie likes to wear light-wicking long underwear made of either polyester or wool. “Those two fibers will stay warm even if they are damp, even if you sweat or become wet.” Patagonia’s Capilene Lightweight Crew ($49) is one of my favorites.
If you suspect the weather may be more relaxed than your sleeping bag can manage, Beattie recommends packing a few more next-to-skin items. “Wear a pair of socks and a fleece hat or beanie you’ll lose a lot of heat through your extremities and head,” she advises. My go-to beanies and socks are the Coal Stanley Hat ($20) and Smartwool’s Ph.D. Outdoor Ultra Light Crew Socks ($20).
If the temperature dips well below your bag’s temperature limit, you can bring a lightweight jacket into the bag and utilize it.
Eric Larsen, a professional adventurer, has skied to the North and South Poles and climbed to the summit of Everest. “I wouldn’t get involved in any disputes about whether or not you should sleep naked. “All I know is that unless it was on purpose and generally with someone else, I have never slept naked in a sleeping bag.”
Larsen is a firm believer in clothing thickly in the cold, a belief he formed from years of sleeping in subzero temperatures. “There is no such thing as a cold night’s sleep; there is only a lack of clothing,” he explains. “When I’m inside the bag, I layer exactly as much as when I’m outside the bag.” Under your suit, you are not nude when climbing Everest. The more heat you can keep close to your body in a warm layer, the better.”
Adaptability is the key. “Make a change if you start to feel cold or hot,” Larsen advises. You are wearing a moisture-wicking next-to-skin layer under increasingly thick insulating layers like a fleece or down jacket, just like layering for the outdoors. The temperature inside the bag may be adjusted more easily with this layering approach.
Finally, Larsen claims that layering encompasses more than what you put on inside your sleeping bag. What’s underneath the bag is also essential. “You can have a lot of layers on, but once those clothing and your sleeping bag are compressed, you’re losing a lot of heat through conduction through the ground.” “It’s like trying to fill a pail with water, but there’s a hole in the bottom,” he explains. Bring a comfortable sleeping pad, such as the Therm-a-Rest NeoAir XTherm ($200) from Therm-a-Rest.
The Middle-Grounders are a group of people who work in the middle of the
Peter Hickner, who founded Feathered Friends, a boutique down gear company, with his wife Carol in 1972, has sleeping bag layering down to a science. “Almost everyone agrees that sleeping bag temperature recommendations are based on someone wearing long underwear,” he explains. To put it another way, a 30-degree bag will only keep you warm down to 30 degrees if you wear it with a base layer. “It’s also a good idea to start with socks, which you can always kick off if it gets too hot.”
Hickner agrees with Beattie on the type and fabric of base layers breathable polyester underwear for the whole you-don’t-want-to-overheat-then-get-cold-with-sweat reasoning.
He is, however, more generous with his employment of extra layers than Beattie. “We highly encourage people to have a sleeping bag that is either barely warm enough or not warm enough, then augment it with clothes inside the sleeping bag,” Hickner says, “under the theory that if it’s cold enough that you’re using a down sleeping bag, you’ve probably got a warm jacket with you, so why not use it?”
The Remainder
What is the one point on which Beattie, Larsen, and Hickner agree? I used to be a sleep-naked supporter, but now I’m solidly on Team Layering. I didn’t strip down on my coldest nights, like when I slept next to a frozen lake in the snow in the Cordillera Blanca or when I had to emergency bivy in California’s the White Mountains. Manage your body temperature to avoid sweating in your sleeping bag.
Hickner’s “augmentation” stance is a happy medium, acknowledging the virtues of both sides (and knowing that it’ll ultimately come down to what climate or conditions you’re camping in).