Sleep Systems: The Part That Decides Whether You Go Again

Buy the pad before the bag

This is the single most useful thing on this site, and it goes against every instinct. Insulation works by trapping air. Lie down and your body weight crushes the fill beneath you until it is nearly solid, and solid material conducts heat efficiently. So the bottom half of even an excellent sleeping bag does almost nothing, while the ground — colder than the air, and effectively infinite — keeps drawing heat out of you for eight hours.

The spec that fixes this is R-value, and it is the one camping number that is genuinely standardized. Since 2020, every pad sold in the US is tested under ASTM F3340: the pad goes between a hot plate at 35 C, standing in for a body, and a cold plate at 5 C, standing in for the ground, and testers measure the energy needed to hold 35 C over four hours at three points on the pad. Because it is one method, the numbers are comparable between brands.

Then read the bag rating properly

Sleeping bags are rated under ISO 23537, published in 2016 to replace the earlier European EN 13537, using a heated manikin fitted with sensors, on a standardized mat, in a climate-controlled room. The test produces two figures: a comfort rating, where a standardized cold sleeper is comfortable, and a limit rating, where a standardized warm sleeper gets through the night curled up. The number in a bag's name is usually the limit.

The gap is about ten degrees, and you can see it on the spec sheets. Kelty publishes ISO comfort 31 F and limit 21 F for its Cosmic Down 20. Marmot publishes comfort 32.2 F and limit 21.6 F for the Trestles Elite Eco 20. Both are “20 degree bags” that are comfortable in the low thirties.

Plenty of camping bags publish no ISO figures at all — Coleman lists the Brazos as 20 F, TETON lists the Celsius XXL as 0 F — and those are manufacturer estimates rather than test results. They are not necessarily wrong; they just have nothing standardized behind them, so leave more margin.

Beds, mats and cots

Sleeping pads, air mattresses and cots fail in different ways. A thick self-inflating pad is warm and comfortable and bulky. An air mattress is the most bed-like and the coldest, because the air inside circulates, carrying your heat to the cold underside and into the ground. A cot is superb on rocky or wet ground and equally cold, because open air moves freely underneath you.

Both cold problems have the same cheap fix: a closed-cell foam pad on top of the airbed or cot. R-values add, so a 14 oz foam pad is a genuine warmth upgrade to any surface.

What we can and cannot tell you

We have not slept in any of this gear. What we have done is compile published specifications, name the standard behind each rating, explain what the test actually measures, and do the arithmetic that turns those numbers into a decision. Where a rating is ISO or ASTM tested, we say so, because the difference between a measured number and an asserted one is the most useful thing a buyer can know. The full method is at how we research.