Therm-a-Rest began as a line of self-inflating camping mattresses, invented in the early-1970s by two former Boeing engineers and avid backpackers.

A Therm-a-Rest self-inflating mattress consists of an airtight nylon fabric envelope filled with a sheet of low density, open-cell polyurethane foam.

When a valve is opened the foam expands and draws air into the mattress.

When the mattress has fully inflated, the user simply closes the valve.

To increase firmness a few breaths of air can be blown into the mattress.