Bivouac sack
The bivouac sack is a windproof, usually also a waterproof sack, which is used as an outer cover around the sleeping bag during overnight stays in the open air, when bivouacking , and protects against moisture, dirt, cooling down by wind and other harmful influences. It is made in versions for one or two people and is mainly used for mountaineering , climbing or trekking . Mathias Zdarsky is considered to be the inventor of the bivouac sack .
Finishes and materials
Simple bivy sacks are made of waterproof plastic (mostly polyurethane / PU). They are light and inexpensive, but have the disadvantage that condensation forms on the inside over the course of several hours , which moisten the sleeping bag underneath. This process is accelerated by a low outside temperature. PU-coated bivouac bags are therefore not suitable for winter use and can only be used for several nights in a row in other times of the year if it is possible to air dry the sleeping bag during the day.
More elaborate bivouac sacks are made from a vapor-permeable membrane (e.g. Gore-Tex etc.) or a laminate (e.g. Sympatex , Hyvent etc.) on the top , which partially allows moisture to escape from the inside to the outside in vapor form, but without letting moisture penetrate from the outside.
Special forms
A bivouac tent is a bivouac sack that also protects the face from rain and wind with the help of a small tent-like structure above the sleeper's head and thus represents an intermediate form between bivouac sack and tent . A windsock is a generously cut bivouac sack in which you can sit upright. Many windsocks offer space for several people in order to make better use of body heat.