This is a US issue Gore-tex "Bivy" sack in a woodland camo print. The bag measures 80" long.

Bivouac sack

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.^[5]

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.^[6] 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.