Use PlatSil Part H Hardener to increase the Shore hardness of any PlatSil Gel. It also increases working and demold time. For PlatSil Gel-OO, a mix of 1A:1B:1H gives a Shore 10A rubber. For PlatSil Gel-10, a 1A:1B:1H mix cures to a Shore 20A rubber. For PlatSil Gel-25, a mix of 1A:1B:1H cures to a Shore 40A rubber. Do not exceed a 1A:1B:1H mix ratio.