HotSac™ VBL – Lightweight Vapor Barrier Liner for Winter Camping

The HotSac™ vapor barrier liner for winter camping is an essential tool for staying warm and dry on cold-weather expeditions. Designed for use inside your sleeping bag, this ultralight liner reduces evaporative heat loss and protects your insulation from internal moisture buildup — a key advantage during extended trips or alpine bivouacs.

By blocking moisture vapor transfer from your body, the HotSac™ keeps your insulation drier and more effective, especially in bags with laminated shell fabrics. In harsh winter conditions, this can be the difference between staying warm or losing critical loft in your down bag.

The HotSac™ does more than standard VBLs. Its reflective gold backing helps retain radiant heat, while the lightweight two-layer ripstop fabric is specially developed to stop moisture and heat loss without adding bulk. The elastic drawcord at the neck seals in warmth and prevents convective heat from escaping during the night.

Weighing just 3.5 oz (101g), the HotSac™ is compact enough to carry in your daypack for use as an emergency bivy sack. Whether you’re winter camping, mountaineering, or planning a multi-day ski tour, this VBL helps protect your sleep system — and your performance.

Stay warmer, sleep drier, and protect your insulation — with the HotSac™, you’re ready for the cold.