Hi,
We're remodeling and the old flooring (lino and carpeting) has been taken up to install hardwood. I noticed many of the 4'x 8' x 3/16" underlayment plywood has lines of stitching. Yes, stitching, which goes through to both sides, and is made of nylon or cotton multi-strand thread.
What is this? I've never seen it before.
TIA