What the @&%# is R-value?

Sleeping mats

Sleeping pads perform two main functions. The first is comfort and the second being to help keep you warm which may surprise many new, and not so new hikers. If you lay on the bare earth, unless it is really hot, the ground will absorb much of your body heat. So in the cooler months of the year you’re going to get cold unless you have an insulating layer to minimise heat loss.

A term you will often hear bandied around when buying a sleeping mat is R-value. But what is it and why should you care?

The R-value that you will see attached to a sleeping mat concerns the insulating benefit of the mat. The higher the R-value, the more insulating benefit you’ll receive. So an R-value of 2 will reduce heat loss twice as well as an R-value of 1. An R-value of 3, will reduce heat loss three times better than an R-value of 1. Simple… right?

The testing process

The term R-value has been around for years but at least as far as sleeping mats are concerned it wasn’t a compulsory standard and some manufacturers estimated the R-value of their mats rather than using a rigorous testing regime.

In 2016 a group of industry leaders in the USA began working on creating a standard methodology to measure and rate the insulation properties of sleeping pads and mats (the ASTM standard).

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. However, it should be noted that this value may not always correlate to actual insulation performance as real-world heat transfer may differ slightly because of additional heat losses possibly involved (for example, edge heat loss, uncovered surface heat loss, compression rate changes or posture changes during sleep).

While, not a perfect system it does mean that consumers now have a way of easily compare mats, at least from a warmth perspective; it’s about comparing ‘apples with apples’ so to speak.

Final thoughts

The level of warmth you need from your sleeping mat is going to depend on the time of the year you will be camping. As a general guide the recommendation is as follow:

  • Summer: R1 to R2.1
  • Spring or Autumn: R2.1 to R3.3
  • Winter:  R3.3 to R5.0+ (with the R5.0+ and above being ideal for extreme cold conditions)

A good-quality sleeping mat has a big impact on your comfort and warmth particularly in colder conditions. Most of us will spend a huge amount of time choosing a sleeping bag and then be a bit stingy when it comes to purchasing a sleeping mat. However, industry recommendations are that to get the maximum performance out of a sleeping bag, you need to have a mat that has an R-value of around 4.0. Surprise, surprise many high end mats have an R-value of 3.8 and this is no accident.

One final comment is that ‘R-value’ only deals with insulation and warmth and doesn’t deal with comfort or features. That’s a whole other ballgame so to find out more read our detailed article on choosing a sleeping pad here.

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