Question

Why is thermal conductivity of plastics is very poor
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Answer 1

Answer:

due to their bond with electrons of plastics. in metals these are loosely packed, therefore they are better conductors

Answer 2

In short, polymers have low thermal conductivity because they have a discrete structure of individual chains. Discontinuities lead to phonon scattering, so even if the backbone is thermally conductive, it is still difficult to make the entire polymer a good thermal conductor.