Self Inflating Mattress

Open-cell foam that pulls in its own air

A self inflating mattress is a slab of open-cell foam sealed inside an airtight shell with a valve. Compressed flat for storage, the foam wants to spring back; open the valve and it expands, drawing air in behind it. The foam adds insulation an air-only mat has to engineer in, and it keeps the mat usable if the shell takes a small puncture; it also weighs more and packs larger. The range runs from narrow singles to doubles and thicker campsite versions.

Does it really inflate itself?

Most of the way, not all of it. Leave the valve open and the foam does the bulk of the work; two or three breaths then firm it up. New mats are slower, and cold air slows them further. Closing the valve while the mat is still soft is why people think one is faulty.

Why does the mat matter more than the sleeping bag on cold ground?

The ground pulls heat out of a body far faster than air does, and the insulation under you is squashed flat by your own weight, so it stops trapping air. A warm bag over a thin mat is the common mistake: the loft above works, the layer beneath does not. Match the mat to the season first, then choose the sleeping bag that sits on top of it. Anyone who sleeps hot can swap that bag for a quilt, which leans on the mat below instead of on loft that gets crushed. A sleeping bag liner keeps the setup clean rather than warmer.

How thick, and single or double?

Thickness decides whether a hip or a shoulder reaches the ground when you turn over, which matters more for side sleepers than back sleepers. Doubles remove the cold strip between two separate mats, at the price of one person feeling every movement of the other. Measure the floor of your tent before ordering a double, because a mat that touches the inner wall of a shelter from camping tents will wick condensation across all night. Where trees allow it, a double hammock sidesteps the floor question, though it still needs insulation underneath for the same reason.

What should be compared between mats?

• Thickness: more foam means more comfort on stony ground and a larger roll to carry.
• Valve type: a wide flat valve fills and empties faster than a small screw valve, which matters most at the packing-up end.
• Shell fabric: a tougher outer resists grit and pine needles, a lighter one saves weight and punctures sooner.
• Shape: rectangular mats give room to move, tapered mats save bulk at the feet where it is rarely needed.
• Packed size: check the roll against the rucksack rather than the weight on the label.

How is a mat looked after?

Store it unrolled with the valve open, so the foam recovers and holds no damp; months compressed cost it loft permanently. Put something between the mat and the ground; most punctures come from underneath. A slow leak shows up by inflating hard and wetting the suspect area, and a patch kit deals with it. A rolled jacket works as a pillow, though a camping pillow stays put better on a slippery shell.