What were those heater types called we used to use before the silicone bed heaters became all the rage? Flat strip resistance material embedded in kapton i believe.

Are you talking about nichrome wire ?

Or PCB based heaters, which are just copper tracks of a calculated resistance.

Yeah, the PC type. "PC heater" did help me find them. They typically are called "flexible polymide heaters" or just polymide heaters. Thanks