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Making sure your sleeping mat is ‘warm’ enough – testing R-Values using the ASTM standard
Ask Baz

Making sure your sleeping mat is ‘warm’ enough – testing R-Values using the ASTM standard

If you have read any of the posts about sleep systemssleeping bags or sleeping mats you will already know that a sleeping mat (or sleeping pad) is not just about providing a comfortable layer to sleep on.

A key function of a sleeping mat is to insulate you from the ground, especially when the ground is colder. To know whether you will sleep warmly it is essential to know how well your sleeping mat resists heat loss into the ground. This resistance is known as an R-Value.

An R-value, tested in a laboratory to precisely-controlled standards, is the only way to know how well your mat will prevent your warmth from being absorbed by the surface you sleep on (a ‘temperature rating’ is simply a manufacturer’s guess – it is not tested)

WHAT IS AN R-VALUE?

Sea to Summit has always provided independent lab-tested R-Values for sleeping mats. Since January 1, 2020, we have used the new industry standard ASTM F3340-18 test to provide R-Values for our mats. This testing standard was created by industry leaders (including Sea to Summit) wanting to achieve two things:

  • Provide clarity and transparency to consumers.
  • Create a universal system to enable users to compare mats across brands.

Both of these points are extremely important to you, the end-user, as you work out which mat from which brand may be most appropriate for the conditions you will be using the mat in. This is very similar to the way that the EN rating system standardized sleeping bag temperature rating tests. Ten years ago, there was absolutely no standardized sleeping bag testing whatsoever in North America, and consumers had to make choices based – in some cases – on guesswork. Since the adoption of the EN rating system, sleeping bags can be compared across brands, even if this comparison is not as perfect as we would like.

HOW DOES THE ASTM R-VALUE TEST DIFFER FROM PREVIOUS R-VALUE TESTING?

The test protocol has more clearly defined things like the ambient temperature or the internal mat pressure during the test. In the case of Sea to Summit, the ASTM R-Value test is very similar to the prior test protocol. 

The value to consumers is that since January 2020, they are able to compare sleeping mats across all brands, knowing that any mat which displays the term ‘ASTM F-3340-18’ next to its R-Value has been tested to a standardized protocol. No more guesswork.

The ASTM-standard R-Value test resulted in some cases to changes to the previously tested R-Values. It’s important to note that where a value did change, it did not signify a drop or increase in warmth—it simply means the mats were tested using a slightly different scale.

WHAT R-VALUE MAT WILL I NEED?

Here’s a simple chart which compares R-Values with external conditions (notice it focuses more on ground temperature than air temperature…)

If you look at our Women’s sleeping mats, you will notice that they have higher R-Values than the Unisex versions. This is because they have more insulation than unisex models. In the case of the Self-Inflating mats, the increased insulation is concentrated into zones in the foot and torso areas of the mat. The higher R-Values quoted for these mats relate specifically to these greater insulation/comfort zones.

Your sleeping mat is the foundation for a good night’s sleep – it’s the first component of your sleep system. Without an insulation level appropriate to the conditions you are sleeping in, the best sleeping bag may just not keep you warm at night.

If you have any questions on R-Value testing, or which mat is most appropriate for use with a given sleeping bag in a specific situation, just – Ask Baz.

8 thoughts on “Making sure your sleeping mat is ‘warm’ enough – testing R-Values using the ASTM standard

  1. avatar Baz says:

    Hi Miguel,

    It is a common misconception that a higher R-Value mat will cause someone to sleep hot when using in the summer. R-Value is a measurement of heat transfer (in sleeping mats we view it as a transfer from your body to the ground,) typically due to internal air movement in the mat. If you think of the insulation in your home, it prevents that heat transfer both in the summer (keeping it out) and in the winter (keeping it in). More than likely, what is making you feel hot is what you have on top of you as well as the ground temperature and humidity of your camping location. Please email info@seatosummit.com with the mat you are interested in, your location of adventure, and your current sleep system and we will be more than happy to provide more information.

    Cheers,
    Sea to Summit Team

  2. avatar Miguel Angel says:

    Probably a stupid question but: does a mat with a high r-value feel hot in the summer? That is, the ambient temperature is high, the floor is warm, better a mat with less r value? The thing is, I don’t care about the weight, and if a mat with a high r-value is not going to make me sweat in the summer (warm sleeper), I prefer to buy this one and use it for the 4 seasons

  3. avatar Baz says:

    G’Day Jean-Sebastien

    You’re absolutely correct: for the Comfort Light Insulated Air mat 4.2 was the R-Value prior to the ASTM standard, 3.7 is the R-Value since the new standard was introduced (January 2020). It’s a great mat, and a firm staff favorite…

  4. avatar JS says:

    Hello ! I just purchased a Confort Light that is rated R 4.2 (what it says on the box) but on your site (and other stores) it seems to be R 3.2. So is this because of the new ASTM R-Value standard ?

    Thank you !

  5. avatar Baz says:

    G’Day Joe,

    We deliberately stayed away from specific temperatures when defining R-Value performance for a couple of reasons:
    - The key factor is the ground temperature, not the air temperature (not an easy metric to come by)
    - Humidity / ground moisture will have a significant effect on heat loss into the ground (humid air and damp ground transmits more energy than dry air and dry ground)
    - The consensus among the manufacturers at the ASTM working group where the new R-Value standard was written was that the focus would be on the tested R-Value, not an estimated correlation to temperature. Clearly, this concept was not maintained outside of the working group.

    As a useful rule of thumb, we often refer to frost. This is because frost forms as a result of ground temperature and humidity in the air:
    - No frost. An R-Value of 1 – 2 is perfectly adequate
    - Light frost. An R-Value of 3 is necessary
    - Hard frost. An R-Value of 4 is necessary
    - Frozen ground without snow cover. An R-value of 5 may be necessary

    R-Value is only a guide to how well an air mat will insulate, by the way – it is a static test, and does not take into account internal air movement and associated warmth dissipation (more pronounced in some designs than others).

    If you would like more details, email us at marketing@seatosummit.com and let us know the conditions you anticipate camping in.

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