Western Mountaineering

Vapor Barrier Liner for cold winter trips

The HotSac VBL is your most important companion for those technical winter trips. A vapor barrier liner (VBL) works by stopping heat loss from evaporative cooling. A VBL will also prevent your body vapor from degrading your insulation. This is most important during extended stays inside your bag. The HotSac VBL goes one step further by stopping radiant heat loss with its reflective metal coating. An elastic drawcord at the top of the HotSac cinches around your neck to prevent convective heat loss. The proprietary fabric is an updated lightweight ripstop. The HotSac weighs only 4.5 ounces and is light enough to carry on day trips as an emergency bivy.