Jackie, some 30 years ago when I started doing hydraulic forming with a friend we used some automotive rubber pad. I think it was a gasket material, perhaps for a truck, about an inch thick and black. It looks almost like rubber tire material but flat and no treads. We cut it into rectangles about 8 cm x 12 cm. It gets scarred up but still works. When the urethane pads were available, I changed to them. Donna in FL