How to store a self-inflating mattress (unrolled, valve open)

Why compression is the problem

A self-inflating mat is a sealed envelope around an open-cell foam core. Exped publishes a 16 kg/m³ open-cell polyurethane foam for the MegaMat; Therm-a-Rest publishes StrataCore urethane foam on the MondoKing 3D; Sea to Summit publishes polyurethane foam in an Air Frame construction; ALPS publishes a Jet Stream open-cell hexagon-cored foam in the Flexcore. All of them work the same way: open the valve, the compressed foam springs back to its own thickness, and air is pulled in behind it. That spring is the entire mechanism.

Leave the foam compressed in a stuff sack for months at a time and the cell walls take a set. The mat still holds air, but it stops inflating itself properly — you find yourself blowing it up or using the pump sack for a mat that used to need neither, and it never quite reaches its published thickness again. There is no repair for it, because nothing has broken: the foam has simply been trained into a smaller shape.

How to store one, step by step

1. Open the valve and let it fully self-inflate. Give it an hour on the floor. You want the foam at its full published thickness — 4.25 inches for a MondoKing 3D, 3.9 for a MegaMat, 5.9 for a MegaMat Max, 4 for a Comfort Deluxe, 2 for a Flexcore — before you do anything else.
2. Wipe both faces and let it dry completely. Damp cloth, mild soap if it needs it, then several hours of air. Both the outside and, if it has been wet inside, the inside — see below.
3. Leave the valve open. All of it: the MondoKing has a two-valve TwinLock system, the MegaMat has two flat valves, the Flexcore XL has double brass valves. Open every one.
4. Store it flat, or loosely rolled. Flat under a bed or on top of a wardrobe is ideal. If you have to roll it, roll it loosely with no strap and no sack — a roll you can push a fist into is fine.
5. Keep the stuff sack somewhere else. The sack is for the trip. Storing the mat in the sack is the mistake this entire guide exists to prevent, and most people make it because the sack is right there.
6. Hang it if you have nowhere flat. Over a rafter or a wide hanger, valve open, so nothing is pressing on the foam. Avoid hanging it from a single point for years; the fabric does not like a permanent stress concentration.

Where to put it

• Dry. A damp basement grows mildew inside the valve and in the seams, and the smell does not come out of a foam core.
• Dark. UV degrades the TPU laminates and polyester shells these mats are built from — Exped and Sea to Summit both publish TPU-laminated fabrics. A mat stored in a sunlit conservatory ages faster than one used twenty nights a year.
• Cool and stable. Not against a furnace, a hot water tank, or directly under an uninsulated garage roof. Heat cycles are hard on adhesive seams and on the foam.
• Off a concrete floor. Concrete wicks moisture up into whatever sits on it. A shelf or a pallet solves it.
• Away from rodents. A mouse nest in a foam core ends the mat. Stored clean and in a hard container, or high up, is the practical answer.

Drying it first, properly

Outside damp is easy. Inside damp is the one people miss, and it happens every time you inflate a mat by mouth — breath carries moisture straight into the foam, where it has nowhere to go.

1. Inflate it with the pump sack, not your lungs, whenever you can. Every mat here ships with one: Exped includes a Top-Up Pump, Therm-a-Rest includes a pump/stuff sack, and Sea to Summit's Airstream HV pump sack doubles as the stuff sack.
2. If it has been mouth-inflated for a week, dry the inside at the end of the season. Open the valve, roll the mat from the closed end to push the moist air out, let it self-inflate with dry room air, and repeat two or three times. Then leave it open and flat for a day.
3. Never put heat into it. No hairdryer, no radiator, no sun. Warm air into a sealed foam envelope is how you delaminate a seam.

The valve, and why it stays open

Two reasons. The foam cannot sit at full loft with the valve shut and some air short — it will be held slightly compressed for the whole storage period. And a sealed mat traps whatever humidity was inside it when you closed it, for months.

The valve is also the part you cannot replace. Exped lists no replacement valve for either MegaMat. Therm-a-Rest sells Permanent Home and Instant Field repair kits but lists no replacement for the MondoKing's TwinLock valve, routing valve problems to its warranty and repair team. Sea to Summit lists no valve or patch kit online at all — parts come by request through its warranty and spare-part form. ALPS sells a Flexcore Repair Kit with two 2-inch patches and adhesive, and no valve. So: a puncture is fixable by anyone, and a valve is a factory job. Treat the valve gently, do not overtighten it, and keep grit out of the threads.

Cot pads and plain foam pads

Not every camp mattress is self-inflating, and the rules differ:

• Cot pads with a removable cover — TETON's canvas camp pad, for instance — store best unrolled and flat, with the cover washed separately and fully dry before it goes back on.
• Closed-cell foam pads such as the Therm-a-Rest Z Lite SOL do not care about compression in the same way, because there is no air exchange and no valve. Store them flat or in their accordion fold; keep them out of sun.
• Air mattresses with an internal pump are a different product again: store them deflated, dry, loosely folded rather than tightly creased along the same lines every time, because repeated hard creases are where the welds eventually fail.

The pad-by-pad rankings are in best cot pads and best sleeping pads for car camping.

Reviving a mat that has been squashed for years

Sometimes it works. The routine is slow and costs nothing:

1. Unroll it, open every valve, and leave it alone on a flat floor for 48 hours at room temperature.
2. Top it up gently with the pump sack — not your lungs — to full firmness, leave it inflated overnight, then open the valve and let it settle again. Repeat two or three times over a few days.
3. Keep it flat and open for a couple of weeks before you judge the result.

If it still does not self-inflate to anything near its published thickness, the foam has taken a permanent set and the mat is now a manual-inflate pad. It will still insulate, because R-value comes mostly from the foam and the trapped air rather than from loft alone, but it will never feel new. That is the cost of the stuff sack.

What the warranties do and do not cover

• Therm-a-Rest: limited lifetime, with a repair-first policy — and Therm-a-Rest may repair damage the warranty does not cover for a reasonable fee, which is the single most useful sentence in any mattress warranty we have read.
• Sea to Summit: limited lifetime against manufacturing defects; spare parts and paid repairs via a request form, charged for labor and materials.
• Exped: five years on defects, a repair kit in the box, a Field Repair Kit sold separately, and repairs in Exped's own workshops including non-warranty damage for a nominal charge.
• ALPS Mountaineering: lifetime against defects in materials or workmanship, with the PVC air bed excepted at one year, plus a line-specific Flexcore Repair Kit.

Every one of those is a defects warranty. None of them is a “you stored it badly” warranty, and three of the four will nonetheless repair your own damage for a fee — which is a better outcome than most camp furniture offers, and still worse than not needing it.

Mats worth storing properly