I use 2 mil plastic from Lowes or Home Depot (sold in 10 x 12 rolls for less than $3). I recently tried 1 mil, and that works just as well although it is obviously not as durable. I only use a footprint to keep dirt off my tent (the ground can be pretty nasty in spots here in the "dirty souf"). A 2 mil footprint for a Tarptent Double Rainbow weighs about 5 oz just as a reference point.