Thermal conductivity is a physical term describing the property of a material to conduct heat or to chill. Materials with low thermal conductivity have lower heat transfer rates than materials with a high thermal conductivity. Accordingly, materials with a low thermal conductivity have thermal insulating properties, keeping the temperature even.
Heat conduction derives from the movement of molecules. High-density materials transfer heat far better than low-density materials simply because more molecules are moving.
Examples of materials with low thermal conductivity include plastic polymers and expanded polystyrene. Steel and aluminum are materials with high thermal conductivity. Steel conducts heat very easily due to its high density, whereas expanded polystyrene has a low density and therefore insulating properties.