Western Mountaineering Hot Sac VBL Sleeping Bag Liner

Contingency plans are important when you launch off on a technical winter trip, where weather can degrade from bluebird to whiteout in a matter of hours and minutes. A vapor barrier liner (VBL) can make a huge difference when you're looking at an extended stay inside your bag, waiting out a storm or cold snap.

A VBL works by stopping heat loss from evaporative cooling, preventing your body vapor from degrading your insulation. This is most important during extended stays inside your bag.

Western's Hot Sac goes one step further by stopping radiant heat loss with its reflective metal coating. An elastic draw cord at the top of the Hot Sac cinches about your neck to prevent convective heat loss. The new Hot Sac, made of a lightweight ripstop, weighs under 4 ounces and packs down to fit into a tiny stuff sack, making it easy to pack on expeditions or bring along on day trips to use in an emergency for signaling, warmth retention, or protection from the elements in nasty weather.