A bivy sack, short for bivouac sack, is the choice for campers who can't or don't want to sleep in a tent. It is an airtight, watertight, windproof bag that goes over the sleeping bag and the user's head. A bivy sack makes a sleeping bag warmer, and lets you sleep under the stars and in places where pitching a tent isn't practical. A bivy sack can be quite expensive, however, so try these steps for making your own.
Cut the Gore-Tex and taffeta so that they are 40 inches across and 2 ½ yards long.
Lay the taffeta on the Gore-Tex with the Gore-Tex inside facing out.
Sew the fabrics together with the seam ½-inch from the edge.
After sewing all around the edges, stop the seam 30 inches from where you started (this is where you will attach a zipper).
Sew the fabrics again along the first seam for extra strength.
Attach the 30-inch zipper or Velcro to the opening on the side. This is where you will get in and out of the sack.
Cut an 8-inch slit in the Gore-Tex and attach the 8-inch zipper or Velcro.
Turn the bag right-side out so the seams are inside. It is now ready to use.