The Gossamer Gear Thinlight 1/8" is a simple closed-cell foam pad made from Evazote EV50 (closed-cell PE foam), just 3 mm thick and weighing 99 g at 130×50 cm. Its R-0.5 insulation rating is given under an older, proprietary standard rather than the unified ASTM test, so comparing it directly to newer pads should be treated as approximate.
Given its weight-to-insulation ratio (around 198 g per R-value unit) and 0.65 m² coverage, it works better as a supplement than a stand-alone cold-weather solution — most commonly placed under an inflatable mattress to protect its underside and add a bit of extra insulation, or used on its own as a minimalist summer pad. With no valve and nothing to inflate, it's essentially maintenance-free and puncture-proof, which also makes it a popular choice as a sit pad or extra floor protection inside a shelter.