The heat transfer coefficient is the transfered heat at 1 square meter area under stable heat transfer conditions through a 1m thick block, both sides of the surface temperature of 1 degree (K, ° C) within 1 second, represented by λ, the unit W / m · deg, w / m · k (W / m · K, here K can be replaced by ° C).The heat transfer coefficient is depending on the material composition and structure, density, moisture content, temperature and other factors. By non-crystalline structure and lower density, heat transfer coefficient is smaller. By moisture and lower temperature the eat transfer coefficient is smaller.