What is R-value on a sleeping mat?

R-value is a measure of resistance to heat flow through the mat, and since ASTM F3340 gave the industry a common test it is one of the few figures in camping kit that genuinely compares across makers. It is also the rare warmth number that adds up when you stack two.

What the figure describes

The mat is what separates you from the ground, and the ground takes heat far faster than still air does. R-value quantifies how much the mat resists that transfer. A higher figure means more resistance.

Since the industry adopted a common test method, values from different makers can be lined up directly — but only when the maker states that the figure is measured to that standard. A number invented in-house is not comparable with a tested one, and it is worth checking which you are reading.

It adds, which almost nothing else does

Stack a closed-cell foam mat under an inflatable one and the resistances add. That is the mechanism behind a habit that looks like overkill: the thin foam mat weighs little, packs on the outside of a pack, cannot puncture, and raises the figure of whatever is on top of it.

It is also a reason not to throw away an old foam mat when you upgrade.

R-value is not thickness

Thickness answers a different question entirely — whether a side sleeper’s hip reaches the ground through a compressed mat. A thick air mat with no internal insulation can have a low R-value; a thin foam mat can have a useful one.

Read both figures, because they fail in different ways. A high R-value on a mat too thin for you is an uncomfortable night; a thick mat with a low figure is a cold one.

Construction changes the feel, not the measure

Air mats are light and noisy. Self-inflating mats are heavier and quieter. Closed-cell foam never punctures and never packs small. The R-value is measured the same way for all three, which is exactly the point of having a standard.

Denier on the base fabric is worth reading alongside it, since that is the face against grit — and an insulated mat with a hole has no R-value at all.

Where it sits next to a sleeping bag rating

A sleeping bag’s comfort figure comes from a different test, on a heated mannequin, under EN 13537 or ISO 23537 where the maker names the standard. Those tests place the mannequin on a mat, which means the bag figure already assumes some insulation underneath.

The practical consequence is that a bag and a mat are a pair, and the commonest reason a bag seems not to match its published figures is the mat rather than the bag. Neither figure is a promise about a given night; both are laboratory measurements for comparing products, and the maker’s own instructions govern how each is used.

What to write down when shopping

The R-value and whether the maker names the standard it was measured to, the thickness, the width and length, the packed size and weight, the base denier, and the inflation method. Then check the R-value against the ground you actually sleep on, and buy the widest mat your pack tolerates — shoulders off the edge of a narrow mat are in contact with the ground, and no rating covers that.

The manufacturer's own instructions come first, and this page does not stand in for them. Every weight, packed length, hydrostatic head, denier, micron rating, lumen figure and temperature on this page is reported from the manufacturer's own documentation, with its unit written as published, and named as such — none of it is measured here. A weight is reported as the maker counts it, and is never restated as another kind of weight, because the two are not the same figure. And the statement repeated rather than assumed: a comfort, limit or extreme temperature is a laboratory figure measured to EN 13537 or ISO 23537 on an instrumented manikin, not a promise about you. How cold a night you can spend is answered by the bag's own instructions, by what you sleep on and wear, and by conditions nothing here can know. Nothing on this site is advice about hypothermia.