Which statement describes thermoplastics' electrical and thermal behavior?

• A. Excellent conductors of heat and electricity
• B. Poor conductors of heat and electricity, but very good insulators
• C. Good conductors of both heat and electricity
• D. Poor insulators

Answer: (B)

Thermoplastics are polymers whose molecular structure doesn’t allow free movement of electrons, and the way heat is transferred through them is mainly by molecular vibrations with limited pathways. This makes them poor conductors of both heat and electricity, so they act as excellent insulators. In their pure form they’re commonly used to insulate wiring, enclosures, and other components because they slow down heat flow and prevent electrical current from easily passing through. (If you add conductive fillers or special additives, some plastics can conduct electricity, but that’s not typical of the standard material.)

This is why the statement describing them as poor conductors of heat and electricity, yet very good insulators, is the best fit. The other options don’t match the general behavior: they are not usually good conductors of heat or electricity, and they are not poor insulators.