Blue Velvet is a two-part silicone impression material consisting of a base and a catalyst or accelerator. The catalyst blends smoothly with the base material by kneading until a consistent blue color is achieved. This material cures in 10 to 15 minutes. This material has minimal shrinkage and distortion. XL-300 has a shore A value and is of medium viscosity. It does not need to be glued to the impression box.