My self-inflating sleeping mat isn't inflating

Inside a self-inflating mat is open-cell foam – think of it like a bath sponge. If you squeeze a sponge flat and then let go, it draws air back in. A self-inflating mat works the same way, except the foam is enclosed in an airtight shell with a valve. When you open the valve, the foam expands and pulls air into the mat.
 

It’s important to note that no self-inflating mat (regardless of brand) will inflate to full sleeping firmness on its own. You’ll always need to add a little extra air – either by mouth or with a pump – to reach your preferred comfort level.

Here's the position the valve should be in for inflation:

First-time use

If your mat doesn’t inflate the first time you open the valve, don’t worry. Mats are vacuum-packed at the factory to save shipping space, and this sometimes causes the foam cells to stick together.

The solution is simple: manually inflate the mat once (by mouth or with a pump sack). This will “unstick” the foam cells, and the mat will self-inflate normally from then on.