Which of the following is NOT considered a good thermal insulator?

A thermal insulator is a material that resists the transfer of heat, making it effective for maintaining temperature differences in various applications, including refrigeration. Metals are known for their excellent thermal conductivity, which allows heat to pass through them easily. This property makes metals unsuitable as thermal insulators.

In contrast, polystyrene, mineral wool, and foam are all materials designed to trap air within their structures, significantly reducing heat transfer. Their composition and physical characteristics provide effective insulation against thermal conduction, making them ideal for use in various insulation applications. Thus, identifying metal as the option that does not serve as a good thermal insulator is accurate.