I use a groundcloth with any tarp or teepee shelter and under my "Platinum" edition BA Fly Creek because the floor fabric is simply too thin, and easily cut.

For floorless shelters I take a hunk of Neatsheet, a discontinued picnic blanket comprising two layers of soft Tyvek (or similar). It's comfortable to sleep on and has withstood moist ground. For my BA footprint I fashioned it from "kite Tyvek" bought through Amazon. This was based on a tip from someone on these forums--didn't know the stuff existed.

I have no idea the fabric unit weight/area but it's light and relatively soft, like jumpsuit Tyvek and not slippery like housewrap. Didn't bother trying to anchor it to the tent pole tips, but that would be ideal.

Cheers,