9' wide Tyvek HomeWrap by the foot, for making tent ground sheets.
Instructions: Cut out the Tyvek to the same footprint as the tent (and optionally, the vestibules), wash in cold water (no detergent), and lay out to dry. The Tyvek should shrink by a couple of inches all around and become soft and flexible. (I suggest cutting the footprint with extended tabs at all tent peg locations and adding small bungee ties with a sheet bend knot. This should help keep the ground sheet centered under the tent.)