This summer’s disturbing string of mountaineering tragedies in the alps, many caused by carrying too little or the wrong gear, got me thinking about shelter. Specifically, lightweight “bivvy” sacks.
|Lisa enjoying life in an Adventure Medical bivvy sack.|
I’ve always liked the idea of carrying some sort of emergency shelter during backcountry travel, though for shorter jaunts in familiar areas I usually leave such items at home. Reason, everything adds up, and an emergency bivvy shelter is just one more small but significant addition to total pack mass.
But I do carry a bivvy sack on occasion, and the less it weighs the more likely I am to haul it.
Thus, it was good the OR show reminded me of two super-lightweight shelter sacks made by Adventure Medical.
Their Heatsheets Bivvy is the one I like best, as it is super light (4 oz) and so small it could be packed inside a medium size first aid kit. More, it comes in a sil-nyl stuff sack that’s thoughtfully oversized so repacking is easy. Adventure Medical also provides a slightly larger and more durable sack called the Thermo-Lite 2 which for only 2.5 ounces more weight is somewhat more durable and perhaps reusable — though in my opinion both sacks are one-time emergency deployment items unless they’re used with utmost care.
One caveat about any bivvy shelter: A thin layer of plastic or nylon provides very little insulation. Heat is lost by air circulation (convection), radiation and conduction. The reflective Mylar plastic of the Heetsheet provides a modicum of reflective insulation but does little to block convection and nearly nothing to prevent conductive heat loss — ditto for most other materials.
Thus, Heatsheet and other thin lightweight bivouac shelters (such as those from Space Blanket)are most importantly a way to stay dry during a stay in the backcountry while waiting for a rescue or spending an unplanned night out. For insulation in such a situation you’ll have to depend on your clothing, so carrying a system of well planned layers is key to safety, as it always has been. More, any group should always consider carrying at least one lightweight synthetic sleeping bag when they venture far from civilization. (At the least, always have a sleeping bag in your trailhead vehicle you can retrieve if you’re skiing nearby laps and someone gets hurt.)
My plan for the winter is to acquire several of the tiny HeatSheet Bivvys and make sure we’re carrying at least one during most backcountry trips. I might even stuff mine in a shovel handle — it is that small.