If you’re in the market for a bivy sack that is roomy enough for inflatable pads and 3/4-season sleeping bags, take a look at the MSR Pro Bivy. It’s one of the lightest waterproof-breathable bivy sacks on the market. It’s strength is simplicity – there are no hoops, poles, zippers, netting. This offers protection for your sleeping bag under a tarp or while cowboy camping. Not recommended for bug season.