Choosing Bivy SacksA bivy sack is a low-profile, waterproof barrier for your sleeping bag that offers an ultra-lightweight alternative to traditional tents. Originally used by climbers who needed lightweight, compact shelters for multi-day ascents, they are also popular among backcountry minimalists who want to shave weight. They don't offer room to move, but they're easy to pack.
The most basic bivy sacks have an opening at the head to let you breathe and allow moisture to escape. More advanced models use mesh panels to keep bugs out.
How to Choose Your Camping Sleep System
Most bivy sacks use two different fabrics to balance protection and weight. The bottom fabric is heavier for durability. The upper fabric is usually lighter and features a waterproof/breathable laminate.
Tips for Choosing a Campsite