The insulating materials commonly used to cover copper wire (and other) electrical conductors fall into two broad classes: Thermoplastic and Thermoset.
What’s the difference?
If we take a look at our Fundamentals of Rome Wire and Cable Manual (yes, it’s from a long time ago but yes, it’s still entirely applicable), we have the following descriptions:
Thermoplastic: This material is one that will soften and even melt when exposed to a sufficiently high temperature. In other words, when the material is originally compounded, it becomes relatively hard yet pliable, much like most plastics we encounter in our daily lives. However, if it is exposed to high temperature at some future time, it softens and melts. The major reason for selecting a thermoplastic material is because it is the most economical type of insulation.
Some of the commonly used thermoplastic insulations used nowadays:
Thermoset: This material, on the other hand, does not soften when exposed to high temperatures. Once it’s compounded and cured, it becomes “rubbery” and retains its properties even when exposed to high temperatures….Thermoset insulations are usually used where the wire or cable will be exposed to high temperatures.
Some thermoset insulations often used are: