Bivouac sacks are available as one-man or two-men versions. The larger models allow a more diverse range of use in rescue operations, but also have a larger packing size. Bivouac sacks are offered in different materials. Models with a very small packing size are made of light, partly coated foil, which are only suitable for emergency storage of victims. These are disposable products, which are usually damaged after use and cannot be folded back to their original size. Nylon versions are somewhat more voluminous, but also more robust and are therefore also used in improvised mountain rescue. Premium bags with a breathable membrane are recommended as soon as the bag is used for several hours in emergency bivouacs. Condensation moisture is carried away to the outside of these models like a good rain jacket, thus preventing a strong moisture infiltration.