New Sleeping Pad R-Value Standard FAQ: ASTM FF3340

R-Value Testing at Therm-a-Rest - Photo courtesy of Therm-a-rest
R-Value Test Machine at Therm-a-Rest – Photo courtesy of Therm-a-Rest.

A New Outdoor Industry Standard

ASTM International passed a new R-Value Sleeping Pad Standard (FF3340-18) last month that will be rolled out to consumers in 2020. It defines a rigorous and reliable methodology for measuring the R-Value of all sleeping pads, including air mattresses, self-inflating pads, and foam pads.

I recently spoke with Brandon Bowers and Greg Dean, both from Therm-a-Rest, about the new R-value standard, and here’s a summary of our conversation. The questions were mine, but I’ve paraphrased their responses below for readability. Any errors in translation are my own.

What problem does the new sleeping pad R-value standard address?

While many manufacturers provide R-Values for their sleeping pads today, there’s never been a consistent way of measuring them so you can reliably compare the insulation value of pads from different manufacturers. The new standard addresses this issue. Those manufacturers who provide R-values for their sleeping pads already will need to test them again to bring their pads into compliance with the new standard. Pad manufacturers that only provide temperature ratings today will probably be required by outdoor retailers to start measuring them and publishing the results. For example, REI and MEC were instrumental in facilitating the widespread adoption of sleeping bag temperature ratings and educating consumers on how to understand what they mean. Both were involved in the definition of the new R-value standard as well.

What are R-Values?

R-Value measures how well an object resists the flow of heat from one side to another. The higher the R-value, the greater the resistance, and the better its insulating properties. When applied to sleeping pads, R-value measures a pad’s ability to keep your body heat from passing through the pad and into the ground. Sleeping pads aren’t designed to be warm, so much as to resist the transfer of heat. Highly insulated pads will usually feel warmer because they keep your body heat close.

What is the new R-Value Testing Process?

The test method measures the thermal resistance of sleeping pads using a two-plate apparatus. The pad is sandwiched between a hot plate and a cold plate and the R-value is measured in three different locations on the pad. The same test is run on three identical pads and the results are averaged together.

Are there any automated testing tools for measuring the new R-values?

Testing hardware for measuring R-values, as defined by the new standard, is already available from a company called Thermetrics. The R-value test methodology and calibration scheme was kept simple to make R-value testing affordable by smaller brands with fewer capital resources to purchase expensive equipment. Hopefully, they will also see the advantage of publishing standardized R-values for their sleeping pads.

How much does a Thermetrics R-value testing machine cost?


Will independent testing labs be responsible for testing sleeping pad R-values or will that be left up to the manufacturers themselves?

It’s too early in the process to know what will be required. The standard was just approved. KSU (Kansas State University), which is lab that does a lot of the sleeping bag temperature ratings for the outdoor industry, has opted not to do R-value testing for sleeping pads because they want to stay focused on their core competency and not dilute it.

Why are R-values a better way to measure insulation value than temperature ratings?

An R-value is a physical measurement that doesn’t require a lot of qualifiers to interpret. For example, don’t have to know whether a person using the sleeping pad is a man or a woman, whether they’re wearing long underwear, or wearing a hat when the test is performed. This makes it very simple for people to understand and compare two pads.

Are R-values additive? Can you stack multiple pads together to create an insulation surface that is the sum of its parts?

Yes, the R-values of sleeping pads are additive, provided that there is no air gap between them.

Which will be warmer: an air mattress placed on top of a foam pad or a foam pad placed on top of an air mattress?

Sleeping pad R-values don’t measure pad warmth, but their resistance to heat loss. As long as there isn’t an air gap between the pads, they’ll have the same additive R-value no matter how they’re stacked.

Does the moisture in your breath, when you blow up a pad by mouth, reduce or alter the R-value of a Therm-a-Rest sleeping pad?

It might have an effect over the long term in extreme temperatures, but it won’t have any effect in normal use.

How does letting some of the air out of an inflatable sleeping pad affect its R-Value?

It might reduce it by 5-10%, but that’s a guess.

Are there any other factors that can reduce the R-value of a sleeping pad after extended use?

Synthetic or feather insulation may compress over time.

What are the different design variables that alter the R-values of Therm-a-Rest’s sleeping pads?

The number of internal chambers, radiant layers, and fabric thickness.

How well do the R-values of Therm-a-Rest’s existing sleeping pads correlate with measurements under the new R-value standard?

Everything will change a little bit because our existing R-value ratings were done in a cold room, which is a different testing environment. But we’ve always used R-values to rate our sleeping pads and we already own a Thermetrics R-value testing machine.

How will the R-values or temperature ratings of other sleeping pad manufacturers be affected by the new R-value standards?

Some manufacturers will have to make major adjustments to their sleeping pad ratings.

Is there agreement on how R-values will be communicated to consumers in manufacturer or retailer product listings? For example, the EN13537 sleeping bag temperature ratings are documented in a standard way across manufacturers and retailers.

Not at this time. Therm-a-Rest will be undertaking a major consumer education campaign in 2019 to help consumers understand R-values and the new R-Value standard.

Philip: Thanks guys. I appreciate the background information and think my readers will find it informative.

Published: 12/2018.

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Author: Philip Werner

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