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Find Out What a Bivy Bag is?
By Hikerpro | May 9, 2009
Bivvy is the non-standard name for a bivouac sack. It is a kind of shelter that looks like a loose sleeping bag. They’re easy to rig up, smaller than a one-man tent, lightweight and waterproof. They’re favored by solo hikers, mountaineers and the military.
Design
A simple bivy consist of a single layer of waterproof material. Early versions of the bivy sack made use of silnylon as the waterproof shell. It is a very light fabric that gives you about another 10 degree fahrenheit extra protection from the elements.
The problem with the earlier versions of the bivy sack is the humidity that condenses on the inside causing users to have wet sleeping bags in the morning. This still happens in some camping tents today. The use of the waterproof/breathable fabric, Gore-Tex, helps to remove some of the humidity while keeping out water from the outside.
Another way that this problem is addressed is by using an inner vapor barrier liner bag or VBL. VBLs prevent body moisture from entering the condensing in the sleeping bag.
Traditionally, bivvy bags have a small hole above the user’s face for breathing. Thanks to Gore-Tex Exchange Lite, an air permeable version of the fabric, the bivvy can be safely zipped up to cover the whole body including the head thus shutting out the elements completely. This new fabric allows both carbon dioxide exhaled by the user and moisture to escape.
Bivvy shelters
In biological terms, the bivy sack is a macroinvertebrate, meaning it has no spine or rigid structure. Bivy shelters on the other hand employs hoops over the head and feet so that the fabric is kept off the user resulting in more breathing room around the head. This also prevents the condensation from soaking into the sleeping bag.
Bivvy shelters weigh a bit more than bivvy sacks but the increased comfort justifies the additional weight. However, bivvy sacks are still favored among mountain climbers and backpackers or adventurers on dangerous expeditions as a compact emergeny shelter.
Popularity
Improvement in bivvy shelters has resulted in increasing demands for this compact shelter. Some like the Outdoor Research Deluxe Bivy have anticlaustrophobic features like a white interior with a shock-corded Delrin hoop for breathing room and 5-foot zippers that allow you to ventilate while keeping you dry.
Bivvies are also popular among carp fishermen who fish throughout the night. This tiny little tent alternative is becoming more advanced and user friendly as manufacturers scramble to make better bivvies in response to the increasing demands.
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