Two-person bivy sack cuts down drafts around our two-person quilt. Center netting section eliminates condensation, 1.1 oz breathable perimeter coupled with staked-out and tensioned bathtub bottom stops drafts from all sides. Drafts from above are typically not a problem, and the netting will block wind to a large extent. Possibly might add 1.1 oz breathable top for coldest weather, connected to top with snaps or velcro.
Make four 5" corner sleeves from coated nylon packcloth or other scrap material
Cut corners of silnylon, form bathtub incorporating corner sleeves
Cut netting, round off top corners, sew perimeter zipper
Cut netting filler pieces to square off netting and sew to zipper
Sew top perimeter pieces to now rectangular netting center piece
