The original rearmost pads from my 32 Tudor are 1 1/2 x 2 5/8 x 5/16 thick. They have six plies of fabric reinforcement. So overall, they consist of mostly the fabric infused with rubber. See photos attached.
McMaster-Carr has some fabric-reinforced neoprene material that seems reasonably close to the original.
https://www.mcmaster.com/catalog/129/4010.