What are the benefits of using a bivy? I don't believe they're very effective as rain protection because the only bivies that are truly waterproof are condensation nightmares from what I understand. Is there any material that is waterproof or close to it and breathes well? I don't think so unless it's some type that's phenomenally expensive. I think Gore Tex's waterproofing/breathability qualities are to an extent hyped. A groundsheet such as Tyvek or Polycro folded over into a pocket that covers the feet is an effective, durable, cheap option that protects against whatever rain may get past the end of a tarp. If a bivy is used to increase warmth or shield form the wind wouldn't a sleeping bag sleeve work better for these purposes, and wouldn't a few ounce net wrapped around the head and suspended from the face be a better option at keeping the bugs and rodents out?