At higher temperatures tellurium is sufficiently plastic to extrude. It melts at 449.51 °C. Crystalline tellurium has a structure consisting of parallel infinite spiral chains. The bonding between adjacent atoms in a chain is covalent, but there is evidence of a weak metallic interaction between the neighbouring atoms of different chains. Tellurium is a semiconductor with an electrical conductivity of around 1.0 S•cm and a band gap of 0.32 to 0.38 eV. Liquid tellurium is a semiconductor, with an electrical conductivity, on melting, of around 1.9 × 10 S•cm. Superheated liquid tellurium is a metallic conductor.