Rebound 40 is an easy-to-use platinum-cure silicone rubber which self-thickens for making brush-on molds of almost any model. Mixed 1A:1B by volume (no scale necessary), Rebound rubber can be applied with a brush or spatula to vertical surfaces without sagging and will cure with negligible shrinkage to a flexible rubber.
Rebound 40 is hard and not very flexible. It is compatible with Rebound 25. For example, you can apply two coats of Rebound 25 and back it up with two coats of Rebound 40.