The mesh is a polyethylene material and many refer to it as Darco. It's a moisture barrier. The only time I've ever had it get damaged is when I had a tire blow out a while back on my old trailer and it ripped that material. There was a void in that area where it ripped, but where it was covering plywood there was no damage. It's pretty tough for the most part, meaning every day use shouldn't cause damage unless something drastic (like a blowout) happens. It's on pretty much every trailer, so it must work fairly well.
