Camping Mattress R-Value: What It Measures and How Much You Need

What R-value is

R-value is a measure of thermal resistance. Therm-a-Rest puts it in one line: the higher the R-value, the more thermally resistant the material is. For a camping mattress, the heat you're losing goes down, from your back into the ground, a cot or a truck bed. Your sleeping bag can't stop that on its own, because the insulation under you is crushed flat by your weight; Therm-a-Rest notes that compressed down fails to create an insulating layer. The mattress has to do that job.

That's why R-value is part of how we score every mattress and pad in our camping mattress hub. It sits in the fit-and-comfort metric, next to thickness and width, and a mattress whose maker publishes no R-value earns nothing for it. The bands are on our methodology page.

The ASTM F3340 test

Before 2019, each brand tested R-value its own way, so a 4 from one maker and a 4 from another weren't the same thing. Work on an industry standard began in 2016, and NEMO says it helped develop it on a committee with other industry partners. Therm-a-Rest says ASTM F3340-18 was finalized and published in 2019, and that it gives an “apples-to-apples” comparison across the sleeping pad market; NEMO says the standard was ratified in fall 2019.

NEMO describes how the test works: it measures how much energy it takes to keep a hot plate at body temperature, with the pad between that plate and a cold surface. The result is a measure of heat flowing one way, from a warm body through the pad to the cold surface beneath it.

How much R-value you need

Sea to Summit's buying guide gives a simple scale:

These are a maker's guidelines, not a guarantee. People sleep warm or cold, a sleeping bag matters, and a cot loses heat differently from the ground. For a buy-once mattress, we'd lean toward more insulation than your typical trip needs: a higher R-value costs you weight and packed size, not warmth on a mild night, and it lets the same mattress cover the cold trips too.

Stacking pads: the numbers add

Both NEMO and Sea to Summit say R-value is additive: put two pads together and you add their ratings. Sea to Summit goes further and strongly recommends adding a closed-cell foam pad to an air mat for winter. Therm-a-Rest says the same of its closed-cell Z Lite SOL: lay it under another pad and it adds R 2.0 and protection from punctures.

That makes stacking the cheapest way to extend a mattress you already own. An R 4.7 air pad plus a Z Lite SOL is roughly R 6.7 on paper. It's also why many cot sleepers carry a thin foam pad as well as a mattress; our guide to staying warm on a cot walks through the layers.

What 17 mattresses publish

Here's every R-value published for the mattresses and pads in our registry, lowest to highest, with the maker's own wording on the test standard.

Two patterns stand out. First, the thick self-inflating mattresses cluster at R 7 to 8.1, well past Sea to Summit's winter line. Second, none of the full-size air mattresses in our registry publishes an R-value at all. If warmth matters, that silence is the answer; see self-inflating vs air mattress for the rest of the trade.

What to look for

• An ASTM figure on the maker's page. It's the only way to compare two brands directly. A number with no stated standard is still useful within that brand, but treat cross-brand gaps of less than a point with care.
• More R-value than your usual trip needs. A mattress rated for winter works fine in summer. The reverse isn't true.
• Foam if you're on a cot or in cold weather. A foam core keeps insulating if the shell leaks.
• A closed-cell pad for the gaps. Stacking is the cheap way to add warmth, and it protects the mattress on top from punctures.

R-value on a cot

A cot changes the math. You're off the ground, but the air under the cot moves, and the cot fabric is a single layer, not insulation. So the pad on a cot carries all the insulation. Our best cot pads rankings list pads by R-value and width, and cot vs sleeping pad covers when you need both. For the full mattress rankings, including where each R-value lands in the score, see our best camping mattresses, and for the rest of the buying decision, how to choose a camping mattress.