Bivvy

A bivvy, short for bivouac sack, is a waterproof and breathable cover that protects a sleeping bag from the elements. It is a lightweight alternative to a tent, offering a minimalist shelter for outdoor enthusiasts. Bivvy sacks are typically made from a single layer of fabric and are designed to be used in conjunction with a sleeping bag and a sleeping pad. They are popular among backpackers, climbers, and alpinists who prioritize minimalism and weight savings.

The primary function of a bivvy sack is to shield a sleeping bag from rain, snow, and wind, while also preventing condensation buildup. The breathable fabric allows moisture vapor from within the sleeping bag to escape, reducing the risk of becoming damp and cold. Some bivvy sacks feature a small hoop or pole to create a headspace, providing more room and preventing the fabric from pressing directly onto the sleeper. Others are simpler, consisting of just a waterproof bag that the sleeping bag is placed inside.

Bivvy sacks are often used in situations where setting up a tent is impractical or undesirable, such as in high winds, on exposed ridges, or during emergency situations. They are generally less expensive than tents and take up less space in a backpack. However, they offer less living space and protection from insects compared to a tent. The choice between a bivvy sack and a tent often depends on the specific needs of the user and the intended environment.