I use cut-up Tyvek race-numbers on the inside. Cut out two pieces, about the size of quarter and nickel. Glue the smaller one one first with 3M Fastak Super Weatherstripping adhesive (follow the instructions on bxo). Then lay the larger one on top. This really thin boot maintains the suppleness of teh sidewall and won't give you a thump-thump-thump ride like thicker stuff. Can also repair sidewall cuts up to 5-6mm as well.