True, but if that is indeed a phase change compound then it is likely high performance.
High performance may well be needed in this application.
My experience with electrical tape and PTFE plumbers tape has been, well, less than stellar. If it has good thermal properties like PTFE plumbers tape, then it doesn't isolate well enough to use above 24 volts or so. It it has good dielectric strength like electrical tape, then you are going to have to use what amounts to an infinite heat sink.
To be honest, I've only tried PTFE plumbers tape twice and electrical tape once. If anybody has any secret homebrew electrically insulating but thermally conducting miracle materal though, I'd love to hear about it.
What is your guesstimate of how many watts you need to dissipate, the voltage it's operating at, and the dimensions of the heat sink?