There are several types of HTMWs made from different types of mineral, and with different properties and temperatures that they can withstand. Below are some common types:
Alkaline earth silicate wool (AES wool)
AES Wool consists of amorphous glass fibres, which are produced by melting a combination of CaO-, MgO-, SiO2 and ZrO2. Products made from AES are generally used in continuously operating equipment and domestic appliances. AES wool has the advantage of being biosoluble; if inhaled it will generally stay in the body only a couple of weeks, reducing the chances of causing silicosis.
Alumino silicate wool (ASW)
Alumino silicate wool also known as “refractory ceramic fibre” (RCF), are amorphous fibres produced by melting a combination of Al2O3 and SiO2, usually in a weight ratio 50:50 (see also VDI 3469 Parts 1 and 5, as well as TRGS 521). Products made of alumino silicate wool are generally used at application temperatures of greater than 900 °C and in intermittently operating equipment and critical application conditions (see Technical Rules TRGS 619).
Polycrystalline wool (PCW)
Polycrystalline wool consists of fibres containing greater than 70 wt.% Al2O3; they are produced by a "sol-gel method" from aqueous spinning solutions. The water-soluble green fibres obtained as a precursor are crystallized by means of heat treatment. Polycrystalline wool is generally used at application temperatures greater than 1300 °C and in critical chemical and physical application conditions, also at lower temperatures.
Kaowool is a type of HTMW made from the mineral kaolin. It was one of the first types of HTMW invented and has continued use into the 21st century. It can withstand temperatures close to 3,000° F (1649° C).