Thermarest Prolite Mattress Added Warmth: A variable pattern of our diagonally-cut foam provides added warmth for cold sleepers. Lightweight: The lightest self-inflating mattress available. Highly Packable: Ultralight, diagonal-cut foam and a tapered shape keep the ProLite mattress extremely pack friendly. Self-Inflating: Expanding foam core self-inflates; top off with just a few breaths for personalized firmness. R-Value: 3.0