Question

what is the best definition of an insulator? an insulator lets heat move through it easily. an insulator prevents heat from traveling through it. an insulator speeds up the flow of thermal energy.

Explanation:

An insulator is a material that has high resistance to the flow of heat (thermal energy). The first option is incorrect because that describes a conductor. The third option is wrong as insulators slow down (not speed up) heat flow. The second option correctly states that an insulator prevents (or at least significantly hinders) heat from traveling through it.

Answer:

An insulator prevents heat from traveling through it.