Sleeping mats matter more than sleeping bags

Treat the sections below as a sequence. With sleeping mats, getting the early decisions right makes the later ones much easier.

The ground takes the heat

Lying down compresses the insulation beneath you to nothing, so the sleeping bag provides almost no protection from the ground. Conduction into cold ground is far more effective at removing heat than the surrounding air is.

This is why people who buy a warmer bag and stay cold are solving the wrong problem. Sleeping bag temperature ratings are themselves measured on a standard insulated mat, so a quoted comfort figure already assumes something underneath it and describes nothing whatever about the same bag used on bare ground.

R-value is now comparable

A standardised testing method means R-values from different manufacturers can now be compared directly. Roughly, low values suit summer, mid values three seasons, and higher values winter and snow. Values are additive, so stacking a foam mat under an inflatable is a legitimate way to reach a winter figure.

Worth knowing before you go — what the figure does not capture is what happens under a hip or a shoulder, since it is measured against a flat plate rather than a body, and a mat you compress to the ground at a pressure point insulates far worse there than its number implies.

Inflatable, self-inflating, foam

Inflatable mats give the most warmth and comfort per gram and can puncture. Closed-cell foam cannot fail, weighs little, is bulky and is markedly less comfortable.

In practice, many winter campers carry both, which covers the failure mode and adds the R-values together. Baffle geometry decides how a mat feels rather than how warm it is, because horizontal chambers tend to cradle a sleeper while a flat, wide-baffled mat rolls you off the side of it, and that is worth discovering before a trip rather than at two in the morning.

Width and length are comfort

A mat narrower than your shoulders means arms on cold ground all night. Short mats save weight and require a pack or clothing under the legs, which works and is worth testing before committing.

In practice, noise matters more than expected in a shared tent, and some constructions are genuinely loud. Shape follows from how you sleep, because a tapered mat suits somebody who lies still on their back and punishes a side sleeper who moves, and the weight it saves is taken entirely from the edges a restless sleeper ends up on.

Field repair

A puncture is the most common serious gear failure on a multi-night trip, and a patch kit weighs almost nothing. Finding a slow leak means submerging the mat or listening carefully, neither of which is easy at night.

Carrying a thin foam mat as backup removes the consequence entirely. Most punctures come from grit carried into the tent and thorns in the ground beneath it rather than from anything dramatic, and the failure a patch kit cannot fix is a valve — which is worth checking before a trip, because it is the one part you cannot improvise on a hillside.

Do not inflate it with your lungs in winter

Breath is warm and saturated, so blowing a mat up puts moisture inside it that condenses against the cold underside and, below freezing, forms ice that displaces the still air doing the insulating. The same moisture feeds mould inside the mat across a season, which is the usual explanation for a mat that has started to smell and cannot be cleaned out. A pump sack fills a mat in a few strokes with dry air, weighs very little and costs a fraction of the mat it protects.

What is underneath matters as much as the mat itself: clearing stones, choosing dry vegetation over bare rock, and treading snow flat and letting it firm up before pitching all change how cold the night is.

The takeaway

Buy the mat before the bag. The ground is what makes you cold.

The route rewards patience more than equipment.