RTV silicone as an insulator?

Has anyone tried using the 500 degree (F) RTV silicone as an insulator for the hot end or heated bed? Is there any reason why this would be a bad idea?

Well there are a few reasons:

1) It's not that great a *thermal* insulator. It's fine for electrical insulation.
2) Some of them are acid cure, which isn't real good for things like brass / aluminum or wires (they give off acetic acid as they cure)
3) Some of them are only rated to 500F on an intermittent basis (that's always hidden DEEP in the fine print)
4) Some hot ends (but no heated beds I know of) go above 260C

I'd say it's a great thing for seating / attaching a thermistor. It's "good enough" as a thermal conductor (much better than an air gap) and you can always pull it apart if you need to.

Permatex red RTV might work. Rated for 600 F continuous. I haven't used it in a printer but we use it a bunch on race cars. One use is as an exhaust sealant not to insulate but to seal leaks.