10 Reasons why Loop-Loc is the BEST Pool Safety Cover The straps have double thick 1 wide polypropylene webbing or reinforcement around the entire perimeter, not just in the corners.No cotton fillers are used in the webbing - cotton, wool or other natural fibers absorb water, become brittle and break.Loop-Loc Safety covers use 80% black to 20% green (4 black stitches to 2 green stitches).