Bivouac sack
（重定向自Bivi bag）
![A bivouac sack (in red) covering a man within a sleeping bag in Benediktenwand, Germany](/Images/godic/202412/24/Bivouac25859.jpg")
![Rock climbing bivouac in Yosemite National Park](/Images/godic/202412/24/Tenaya_bivouac_085345859.JPG")
A bivouac sack (also known as a bivy, bivvy, or bivi) is an extremely small, lightweight, waterproof shelter, and an alternative to traditional tent systems. It is used by climbers, mountaineers, hikers, ultralight backpackers, soldiers and minimalist campers. The bivouac sack has a larger, similar counterpart, called a bivouac shelter.