Introduction: Self-inflating mats revolutionised backpacking when they were introduced by Thermarest over 30 years ago. They are made by sandwiching a sheet of foam between two nylon sheets and adding a valve. When you open the valve the foam expands and sucks air into the mat and after a few minutes the mat is inflated. I usually find you need to add a few breaths by mouth to get it to a comfortable level. These mats are pretty light and comfortable, though less comfortable than insulated airbeds.
Comfort: Self-inflating mats are pretty comfortable but as a general rule comfort of a camping mat is proportional to its thickness - so the thinnest mats will be less comfortable than their thicker counterparts.
Cut-outs: In order to make self inflating mats lighter some manufacturers have punched holes in the foam - removing material from the mat without compromising comfort - obviously there is a limit to how far you can go without destroying the integrity of the mat - but designers seem to have got it right - they have lightened the mats without affecting performance.
Self Inflating versus Insulated Airbeds: Insulated airbeds would seem to have its all! They are more comfortable, slightly lower weight and slightly lower packsize than self inflating mats, however there are a few reasons why some people prefer self-inflating mats:
What to look out for: