A forumite turned me on to "kite" Tyvek, similar to housewrap but a bit thinner with a soft finish--not crinkly. I don't typically take footprints but use this stuff with floorless shelters and beneath my Fly Creek Platinum, which has floor fabric simply too thin for anything but forest duff and meadows.

Available from Amazon in varying lengths. One bolt is basically a lifetime supply.
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--Rick