 In thermal conductivity, "k" is defined as "the quantity of heat, "Q", transmitted in time ("t") through a thickness ("L"), in a direction normal to a surface of area ("A"), due to a temperature difference (Δ"T") [...]".Thermal conductivity is a material "property" that is primarily dependent on the medium's phase, temperature, density, and molecular bonding.Thermal effusivity is a quantity derived from conductivity, which is a measure of its ability to exchange thermal energy with its surroundings.