Alumilite's High Strength 1 silicone mold making rubber has a higher durometer than the other High Strength silicones from Alumilite but still maintains the exceptional tear strength which makes it great for one or two piece molds that require a higher hardness. The High Strength 1 measures a 38A shore hardness. The High Strength 1 is a tin base silicone and cures against all different types of clay and substrate without inhibiting. The tin base silicone is a condensation cure and therefore temperature and humidity may affect the cure speed of the rubber. The High Strength 1 has a low viscosity which does not require degassing (always recommended when available) and will pick up the exact detail of your original. Use the High Strength 1 when you need a little more stiffness to your mold but still desire an exceptional tear strength. Use Alumilite's Rubber to Rubber mold release or petroleum jelly when making 2-piece molds when using the High Strength 1 rubber due to it's extremely high tear strength.