Mud flap, .125 thick Urethane x 12" x 18", Each, 85A Shore.
This is the same material used by the WRC. Very tough. Pieces are just rectangles. It is up to you to shape the piece and put the holes in. Use large washers around bolts. Avoid sharp corners where tears can start.
MFBK - Black
MFRD - Red
Mud Flaps are sold each at the price shown. 1 is required per wheel protected.