Perlite is not a trade name but a generic term for naturally occurring siliceous rock. To make perlite insulation, perlite ore is crushed and segregated. Then it is heated to a point in its softening range where its volume expands some 4 to 25 times due to the 2 – 6 % combined water in the ore. When rapidly heated to above 870°C (1600T), the ore pops as this water vapourizes, creating countless partial vacuum air pockets in the heat softened glassy particles which makes expanded perlite lightweight and an excellent insulator.