There are a lot of “ultralight bivy sacks” on the market that are made with water-resistant (and not waterproof) fabrics designed to keep rain spray, condensation, spindrift, and wind off your sleeping bag while sleeping under a tarp or other floorless shelter. However, we really like the Borah Gear Ultralight Bivy for mild weather conditions where bugs are extreme and temperatures are warmer. There’s more mesh at the head end, and you’ll get less condensation and more comfortable breathing than when using a bivy with more fabric in the head end. It’s also one of the lightest DWR bivies on the market.