Therm-a-Rest Women&#39;s Trail Pro (Regular) The Toughskin's design sandwiches the mattress's air-holding seal between a top layer of open-cell foam Expandable Foam: Our patented expandable foam helps create a lightweight, compact core without waste. Weight: 880 grams (1lb 15oz) Thickness: 5cm(2 inches) R-Value: 5.1 Bottom layer of closed-cell foam, then joins them all with our guaranteed foam-to-fabric bond.