The problem with bivies seems always to be that the foot section of the bag/quilt gets wet from insensible perspiration. Opening the foot helps. I don't think anyone has found an effective balance of breathability and water resistance, although IMHO, Driducks comes closest if you put a drawstring closure with a spinthrift collar on it. Then it can be left open unless you are in cold, dry weather. The collar will keep water out in a deluge.