This is a US issue Gore-tex "Bivy" sack in a woodland camo print. The bag measures 80" long.
A bivouac sack is a smaller type of bivouac shelter. Generally it is a portable, lightweight, waterproof shelter, and an alternative to larger bivouac shelters. The main benefit of a bivouac sack shelter is speed of setup and ability to use in a tiny space as compared to tent-like shelters. A bivouac sack is therefore a common choice for hikers or climbers who have to camp in tight areas, or in unknown areas. A bivouac sack will usually have a thin waterproof fabric shell that is designed to slip over a sleeping bag, providing an additional 5 to 10 °C of insulation and forming an effective barrier against wind chill and rain.
A drawback of a simple bivouac sack is the humidity that condenses on the inner side, leaving the occupant or the sleeping bag moist. Moisture severely decreases the insulating effect of sleeping bags. This problem has been alleviated somewhat in recent years with the advent of more waterproof/breathable fabrics, such as Gore-Tex, which allow some humidity to pass through the fabric while blocking most external water. A traditional bivouac bag typically cinches all the way down to the user's face, leaving only a small hole to breathe or look through. Some modern fabrics are sufficiently gas-permeable that they can be safely zipped up around the user's head in order to shut out the elements completely. Other bivouac sack have a mesh screen at the face area to allow for outside visibility and airflow, while still protecting from insects.