Made of EPDM. So probably only designed for 200 or 300 degrees. Works great in my engine bay about 8 inches above the exhaust manifold. Silicone couplings are rated for 500 degrees. I've also bought silicone cases and found them to be just as flexible and easy to use as EDPM. The kit also includes hose clamps, not silicone clamps. Given the choice, I would prefer these silicones unless heat would be an issue.