Emissivity 

 Emissivity is a thermocynamics term. It is The ability of a surface to emit radiant energy compared to that of a black body at the same temperature and with the same area. In simpler words, it is the ability of a material to hold or release heat.

Don't confuse emissivity with conductivity, however, which is the ability of heat to transfer through a material. Metallic materials have high conductivity but low emissivity when left uncoated. 

For example, three baked potatoes are wrapped in three different materials: aluminum foil, coated aluminum foil, and paper. Both the paper and the coated aluminum foil have high emittance and the potatoes cool more quickly than the potato wrapped in aluminum foil.

Back to glossary