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Material Science: Everything You Need to Know About Sleep Systems

A version of this story appeared in the summer 2020 issue of Uncommon Path

The Sleeping Bag

Many bags you’ll find at REI come with two temperature ratings: one for comfort and one for a lower limit. The labeling looks like this.

sleeping bag ratings

Of course, know thyself. If you run a bit colder, consider a bag’s comfort rating your personal lower limit.

Comfort Rating (T-Comfort): If the ambient air temp outside is this number or higher, a cold sleeper should be comfortable (assuming you’ve paired your bag with the right pad; see right).

Lower-Limit Rating (T-Limit): If it’s colder than this lower temperature, even a warm sleeper may be chilled.

 

The Sleeping Pad

When you crawl into your sleeping bag, you compress the insulation. That, combined with the cold ground, is a recipe for a shivery night. So, yes, your pad cushions you from rocks and roots, but its most important job is to help you retain your body heat, which is measured by its R-value.

R-Value: This value measures your pad’s thermal resistance, or its ability to prevent heat loss. Most camping pads live somewhere between 2 and 6, with the higher numbers being more insulating.

 

The Sleep System

Your bag and your pad create your sleep system. Seems simple enough, but neither actually works as advertised unless paired properly. Our sleeping bags are all tested on a surface that’s about the equivalent of an R-value of 5.4. A sleeping pad with an R-value of 5.4 is considerably warm and often reserved for winter camping. Chances are, you’re not using a pad as warm for three-season camping—which means your bag’s temperature ratings won’t be accurate. Use this chart to pick the right bag and pad for you.

sleep system chart

REI Co-op member Bilen Beck (below left) sleeps cold, so she’d love the electric-blanket-like warmth of this sleep system: Her stacked pads give her an R-value of 6.2, meaning she’ll feel cozy at her pad’s comfort rating.

REI Co-op member Samuel McDonald (below right) is a warm sleeper. The 4.2 R-value of his pad should make his quilt comfortable just above 30°F. But if he gets too hot, he can always stick a leg out or fold the quilt over like a comforter.

sleep systems

Bilen’s Sleep System

Pad R-values are additive: Consider layering two for extra warmth if you run cold. The inflatable Sea to Summit Comfort Plus SI is 4.1. The closed-cell foam Therm-a-Rest RidgeRest SOLite is 2.1. Boom. Now Bilen’s at a winter-ready 6.2.

Unless you’re trying to protect your inflatable from punctures, put the foam pad on top, closer to your body, for a more comfortable night. Foam is quicker to warm up with your body heat than 3 inches of air.

Sam’s Sleep System

Quilts are great for summer camping and folks who run hot. But because they lack bottoms and hoods, they can’t be tested like other sleeping bags. If a bag doesn’t advertise the test ratings, you’ll see a temperature rating, which is the brand’s honest assessment after much (non-standardized) testing.


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