Insulators?
Answer:
Vacuum is a good insulator since conduction and convection are absent and highly silvered surfaces prevent radiative transfer also to a large extent.
Air is a poor conductor compared to a liquid or a solid since the density and hence the number of molecules available for heat transfer are less. So, most of the insulators like thermocole, refractory bricks etc. depend on a high amount of porosity for achieving insulation properties.
In a solid, thermal and electrical conduction depends on the free electrons (electron cloud). Non-metals and ceramics are poor conductors of heat compared to metals.
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