Therm-a-Rest is a trademarked name for a line of self-inflating camping mattresses. They were invented in the early 1970s by two former Boeing engineers, who were avid backpackers. They named their company Cascade Designs.
A Therm-a-Rest air 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. To pack the mattress, the valve is opened and it is rolled up tightly to force the air out, whereupon the valve is closed to prevent re-inflation. There is a slight weight penalty in such mattresses compared to non-inflatable pads, but Therm-a-Rest does sell a line of easily compacted non inflatable pads at a much lower price. Open-cell inflatable pads can provide insulation from cold and hard surfaces more efficiently than non inflatable pads. Therm-a-Rest also offer mummy bags, sleeping bags, and seating.
Similar mattresses are now available from competitors.
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