The max temp ratings I'd seen(way back when), for Viton and silicone O-rings, were 392 and 400 degrees Farenheit, respectively. Not far enough apart to make much diff, I thought. I've still got a package of the Vitons, from the original order, that I've never had to use, 'cause the ones in service stayed supple, and elastic. I've never actually used an IR thermometer, to see what kind of temp output tubes generate. I'll have to find now(all this has me curious).