By Hugh Owen and Maggie Slepian
All sleeping pad R-values are created equal. Right?
Wrong.
Until 2020, sleeping pad manufacturers assigned R-values to their pads using an array of nonstandard testing. Some manufacturers assigned temperature ratings.
But starting this year all sleeping pad manufacturers began using the same testing method to assign R-values to pads. As a result, the R-value for some pads increased, while it dropped for others, although no structural changes were made in the pads.
As an example, the R-value for Therm-a-Rest’s popular NeoAir Xlite increased from 3.2 to 4.2 for the men’s pad. Same pad, same cold weather protection, though.
What is R-Value?
R-value is a measure of thermal resistance, or how well a material insulates against heat transfer. With a sleeping pad that means the higher the R-value, the less heat from your body gets sucked through the pad to the cold ground.
Several years ago manufacturers collectively agreed to a standard measurement for R-value, called the ASTM F3340-18, and began using it for sleeping pads sold in 2020. It’s important to note here that R-value did not change, just the way that manufacturers were testing for it.
So now consumers can compare sleeping pads based on a standard measurement of R-value, without a dizzying array of temperature ratings and R-values arrived at through nonstandard testing.
But be aware that there’s no standard for R-value that will make you comfortable at a certain temperature. Some people sleep warm, others sleep cold.
But there are rough guidelines:
Summer: R1 to R3
Three season: R3 to R5
Winter, four season: R5 plus
How are the ASTM R-values tested?
R-values (resistance to heat flow) are measured by placing a hot plate on one side of a sleeping mat and a cold plate on the other. Electronic sensors then determine how much energy it takes to keep the hot plate at a consistent body heat.
Most major sleeping pad brands are following the new standard, but you can be sure by checking for the ASTM seal for any pad you buy starting last year.
If you camp in different seasons, it’s good to know that R-values are additive. So an R2 closed-cell pad under an inflatable R3 pad would give you an R-value of 5 as long as there is not significant air flow between the two pads.
Remember to factor in your sleeping bag when determining what R-value pad to use. Therm-a-Rest says that a pad with a 4 R-value is necessary to get the full warmth from a sleeping bag. This means that a pad with an R-value of 3 might not give you the full comfort of a 20-degree bag. But an R-value of 6 might let you sleeping comfortably in a 20-degree bag if the temperature drops below that.
Other factors to consider are clothing you wear inside your sleeping bag, ground temperature, whether you sleep on your back (warmer) or on your side (colder), and if you’re on a tent platform or shelter floor with cold air flowing underneath.
What R-value do you need?
In general, a 4 R-value pad (the NeoAir XLite is a good example) might be the best choice. Combined with a 20-degree bag, that gives you good protection for three seasons. After that, mix and match to stay warm: wear more clothes, add a sleeping bag liner, or add a 1 or 2 R-value mat for winter camping. In summer, carry a 40-degree bag or a lightweight quilt.
Our picks for sleeping pads, by R-value
Therm-a-Rest ZLite Sol (Warm weather, closed-cell foam)
R-value: 2
Weight: 14 ounces
MSRP: $45
This is the classic closed-cell foam pad. Not as cush as inflatable, but virtually indestructible.
Sea to Summit UL Insulated Women’s (3-season, inflatable)
R-value: 3.5
Weight: 15.8 ounces
MSRP: $140
Takes far fewer breaths to inflate than the NeoAir line, but weighs slightly more with less padding.
Therm-a-Rest NeoAir XLite (3+-season, inflatable)
R-value: 4.2
Weight: 12 ounces
MSRP: $190
The most popular inflatable pad for backpacking. New valve takes less effort to inflate, but it can be noisy at night.
Therm-a-Rest NeoAir XTherm (Winter, inflatable)
R-value: 6.9
Weight: 15 ounces
MSRP: $220
One of the warmest pads out there with an insane warmth-to-weight ratio. Lots of breaths to blow up, can be loud.