The American Society for Testing and Materials F3340-18 standard is a standardized way in which backpacking sleeping pads are measured for r-value, or their warmth and insulation value. As a standardized test this allows one to compare sleeping pad r-values on a level field. The test utilizes a cold plate underneath the sleeping pad being tested, with a near-body-temperature warm plate placed on top. Inflatable sleeping pads are inflated to the same inflation pressure. The amount of energy it takes to the keep the plate at a constant temperature on top of the pad is measured, and a corresponding r-value is then assigned to the sleeping pad.

Comparing ASTM-F3340-18 r-values allows backpacking sleeping pads to be compared on a more level playing field.

Applying ASTM F3340-18

While the r-value number itself is very useful once you know what r-value has been working for you in various conditions, the standard also features a chart with relatively vague assignments such as “All Season” or “3-Season” as well as a “Variance Zone” – instead of specific temperature ratings. Thus, personal experience with various r-values and sleeping pads across a wide range of conditions is the best knowledge to have (combined with ASTM test r-values), when it comes to shopping for your next sleeping pad.

Ways to Boost R-Value

If you’re getting a bit chilly on those shoulder season or winter backpacking trips taking a warmer sleeping pad is of course a good option. However, another way to help is to take along a foam pad to combine your inflatable or to add to your existing foam sleeping pad. Stacking these pads adds warmth and in my experience, it can be surprising how much warmth even a thin foam pad can add. Options include the ULA Siesta foam pad or something like this option at Amazon.com. Or for more warmth, the venerable Therm-a-Rest Z Lite is a packable (and much warmer) option.

Colder conditions call for a higher r-value, and this can be achieved either through dedicated cold-weather sleeping pads or by way of a system utilizing multiple sleeping pads.

More Reading

For more on sleeping pads, see our articles on closed cell foam (CCF) backpacking sleeping pads as well as multi-purpose foam backpacking sleeping / sit pads, and for even more on r-values and sleeping pads in general, check out our post on choosing the best backpacking sleeping pad.

Editor’s Note: This article originally appeared in Issue 53 of TrailGroove Magazine. You can read the original article here.