Bivy sacks were first developed as solo shelters for mountaineering, climbing, ultralight backpacking and adventure racing where participants were interested in light weight and highly compressible gear. The original bivies were little more than waterproof sleeping bag covers that protected extreme athletes from rain or provided them with a temporary emergency shelter.
However, in recent years, a new class of bivy sacks has evolved that incorporates high tech breathable fabrics like Gore-Tex and eVent with elements of ultralight tents such as mesh screening and collapsible vestibules. Initially, these more advanced bivies were manufactured by a few specialist and cottage brands such as Integral Designs, Outdoor Research and Bibler (acquired by Black Diamond), but mass market manufacturers such as Marmot, Big Agnes, Mountain Hardware, REI, The North Face and MSR have introduced models in recent years, reflecting an increased audience for this class of solo shelter.
This video illustrates the bivy’s evolution into a more comfortable solo shelter with the addition of a mesh screen and collapsible poles to improve ventilation and keep the screen off the user’s face. This bivy has a Gore-Tex top to reduce moisture built-up in your sleeping bag from sweat. This is particularly important in winter when trapped sweat can significantly reduce the thermal efficiency of your bag.
Sleeping in a bivy sack is an acquired taste and not for everyone. Given their space constraints, there’s not much to do except sleep once you’ve gotten into one. Still, they provide an excellent way for you to eliminate the weight and bulk of a tent, particularly in winter, if you are mountaineering or climbing, and need to carry a lot of other gear and food.
That said, they are a terrible shelter choice if you want a shelter that lets you do anything except sleep. In that case, you’d be much better off with a proper tent or tarp tent despite the weight increase.
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