The thermal conductivity of a crystal can depend strongly on isotopic purity, assuming other lattice defects are negligible. A notable example is diamond: at a temperature of around 100 K the thermal conductivity increases from 10,000 W · m · K for natural type IIa diamond (98.9% C), to 41,000 for 99.9% enriched synthetic diamond. A value of 200,000 is predicted for 99.999% C at 80 K, assuming an otherwise pure crystal. The thermal conductivity of 99% isotopically enriched cubic boron nitride is ~ 1400 W · m · K, which is 90% higher than that of natural boron nitride.