My self-inflating sleeping mat isn't inflating

The inside of the sleeping mat is open-cell foam; in essence, it is just like a bath sponge. If you were to squeeze a bath sponge flat in your hand, it would draw itself full of air once you released your grip. Exactly the same thing happens in a self-inflating mat, except that the 'sponge' has an airtight skin around it with a valve. Once the valve is opened, the foam core will draw air into the mat.

It is important to know that a self-inflating mat (regardless of brand) will not self-inflate to the degree of firmness necessary for sleeping on - you will always need to add a little extra air (either via mouth inflation or with a pump) to bring the mat up to the pressure you will want.

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

If you find that your self-inflating mat does not draw air into itself the first time it is used, here is what is happening:​

The sleeping mats are vacuum-packed at the factory to save on space and thus on shipping costs. This sometimes causes the individual cells of the foam to stick together, so that when the valve is opened for the first time, the mat may not inflate.

If you manually-inflate your mat (either by mouth or using a pump-sack), the cells inside will unstick and the mat will self-inflate the next time you use it