This video shows how Flexer™ is used in conjunction with a rigid castable epoxy to make the resultant casting flexible.
Flexer™ Epoxy Flexibilizer is a clear, low viscosity liquid additive that will lower the durometer (Shore hardness) of some Smooth-On casting and laminating epoxies. When added to the epoxy system in the proper proportion, the cured epoxy will be softer and, in some cases, can be made semi-rigid.
Flexer™ lowers the viscosity of the epoxy system and improves wetting capability (for laminating) and filler load capacity.