On a cold night the ground takes more heat from you than the air does. The down underneath you is crushed flat by your weight, so it adds very little. What stops the ground drawing the warmth out of you is your sleeping mat, and its R-value tells you how well it does that job.
What an R-value measures
R-value is thermal resistance: how well a material resists heat flowing through it. The higher the number, the warmer the mat. The scale is linear, so an R 4 mat resists heat flow twice as well as an R 2 mat.
R-value says nothing about comfort, weight or thickness. Our egg-crate foam mat is 2 cm thick, while our car-camping mat is 10 cm. Choose the R-value for warmth, then the type of mat for comfort and packing.
The ASTM F3340 standard
For years every brand measured R-values its own way, and the numbers couldn't be compared. ASTM F3340-18, a standard test method finalised in 2019, changed that, and most major mat brands have used it since 2020.
The test places the mat between a heated plate at 35°C, standing in for your body, and a cold plate standing in for the ground. Air mats are inflated to a set pressure. The lab measures how much energy it takes to keep the heated plate at temperature: the less energy needed, the higher the R-value.
Not every brand uses it. Of the mats we sell, only the foam mat has a published R-value (2.5 with its foil face, 2.1 without: the maker's figures), and the maker doesn't say it comes from ASTM F3340 testing. Where a mat doesn't publish an R-value we treat it as a warm-weather mat unless you stack it on foam; our winter air pad lists R 7.6.
What R-value you need, by season
Seasonal guides vary from brand to brand, and the temperature of the ground matters more than the air. As a rough guide:
| Conditions | Overnight lows | R-value to look for | What we'd use |
|---|---|---|---|
| Summer, warm nights | Above about 10°C | Up to about 2 | The foam mat (R 2.1 to 2.5), or an air pad on a warm night |
| Three seasons | About 0°C to 10°C | 2 to 4 | The foil-faced foam mat (R 2.5), with an air pad on top for comfort |
| Frost, and winter below the snowline | About 0°C to −10°C | 4 to 5 | Our winter insulated air pad (R 7.6), or an air pad on the foil-faced foam mat, plus a warm bag |
| Snow | On snow, or below about −10°C | 5 or more, 6 or more if you sleep cold | Our winter insulated air pad (R 7.6) on the foil-faced foam mat |
Cold sleepers, and anyone camping on frozen or wet ground, should aim for the top of each range. Every one of our sleeping mats lists the maker's R-value where one exists, plus its weight and size.
Stacking mats: R-values add
R-values add together. Lay an R 2.0 foam mat under an R 3.6 self-inflating mat and you're sleeping on about R 5.6. That's how many walkers make a three-season mat work in winter without buying a second inflatable.
- Our air pad on the foil-faced foam mat: at least R 2.5 plus whatever the air pad adds, for about 930 g.
- The 10 cm self-inflating mat on the foam mat: a warm, soft bed for car camping on cold ground.
- Any air mat on foam: the foam also protects the air mat from sharp ground.
Put the foam mat at the bottom. It shields the inflatable from rock, sticks and spinifex, and if the air mat goes flat in the night you're still off the ground. The sums use the maker's figures, so treat the totals as approximate.
Foam, self-inflating or air?
Closed-cell foam
It can't puncture, needs no inflating, and doubles as a sit mat at lunch. It's bulky and firm, so it rides on the outside of your pack, and most side sleepers want something softer on top. Our egg-crate mat is 2 cm thick: 330 g with its foil face (R 2.5), or 280 g without (R 2.1).
Self-inflating
Open-cell foam sealed inside an airtight shell. Open the valve and the foam draws air in, then top it up with a breath or two. It's quieter and steadier than an air mat, and still gives some cushioning if it springs a leak. Our 10 cm self-inflating mat is a car-camping mat: about 195 × 70 cm and 1.1 kg, with a built-in foot pump. Store it unrolled with the valve open so the foam keeps its spring.
Insulated air mat
The thickest and most compact for its warmth, but it relies on staying inflated. Our air pad with pillow is about 190 × 60 cm and 600 g, with a built-in foot pump so you don't blow damp breath into it. Carry a repair kit.
Getting the most from your mat
- Clear sticks and stones from under the tent before you pitch.
- Air contracts as it cools, so an air mat pumped up in a warm tent can feel softer by the early hours. Top it up before you settle in.
- If you roll around at night, a wider mat keeps you on the insulation. Our 10 cm mat is 70 cm wide.
- On frozen ground, don't rely on a single air mat: a foam mat underneath is cheap insurance.
Your mat and your bag's rating
Sleeping bag temperature ratings assume a good mat. In the ISO 23537 test, the manikin lies on a foam mat of roughly R 4.8. On a thinner mat, your bag won't reach its rating. Our temperature ratings guide explains how the test works.
Quilts depend on the mat even more, because there's no bag underneath you at all. Below freezing, put R 4 or more under any of our down quilts, and see quilt vs sleeping bag for the rest of the picture.
Before a cold trip
- Check the forecast for where you'll camp, and the park's alerts and closures. Our Australian conditions guide has typical overnight lows by region.
- Snow camping takes experience and far more than a warm mat and bag: a four-season tent, navigation skills and a plan for bad weather.
- Pack the rest with our overnight hike checklist.
Sources
- ASTM F3340-18, Standard Test Method for Thermal Resistance of Camping Mattresses.
- Published explainers from mat makers on ASTM F3340: the test conditions, when the standard was ratified, and additive R-values.
- ISO 23537-1:2022: the test mat used for sleeping bag ratings.