A Bivy, or Bivouac Sack is a bag for your sleeping bag. In good weather, they keep your sleeping bag clean, in bad weather, they keep you dry (mostly)... Bivys are basically a waterproof shell that protects your sleeping bag. They have an added benefit of keeping dew off your sleeping bag, and slightly increasing your warmth. The only down-side is that the bag will trap moisture (perspiration) in the bag. In hot/humid conditions, this can be a big problem.
In this Instructable, I'll show you how to make a cheap bivy that works well in decent weather and is not terribly heavy. In rainy conditions, you should have additional shelter over you. (Commercial Bivys start around $80.)
This bivy is constructed from 14'-15' of 3' wide Tyvek House Wrap, and double-sided carpet tape. The basic design is a full length of tyvek folded at the foot and sealed on the sides.
One important note: This bivy does not breathe. Never seal up an unvented bivy over your head!
Step 1: Materials/Tools
Approximately 15' of 3 foot-wide Dupont Tyvek Home Wrap (or similar).
Double-Sided Carpet Tape (the permanent kind)
Tyvek Tape (optional)
Wallpaper seam roller (Optional)
Build Time: Approximately 2 hours, with a break for drying the tyvek...