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The COCOON Vapor Barrier Liner surrounds your body with an ultralight, 100% non-breathable 15 Denier Ripstop Nylon shell that is laminated with a TPU-film on the inside. Ideal for long winter trips under extremely cold conditions, the technical liner minimizes evaporative heat loss and reduces dehydration. It helps to maintain the insulation and the loft of your sleeping bag by protecting it from body moisture. The Vapor Barrier Liner also makes a great emergency bivy.