The classification temperature is defined as the temperature at which a linear shrinkage of a certain amount (usually 2-4%) is not exceeded after a 24‑hour heat treatment in the electrically heated laboratory oven and in a neutral atmosphere. Depending on the type of product, the value may not exceed the following limits: 2% for boards and shaped products, 4% for mats and papers.
The classification temperature is specified in 50 °C steps (starting at 850 °C and up to 1600 °C). The classification temperature does not mean that the product can be used continuously at this temperature. In the field, the continuous application temperature of amorphous HTMW (AES and ASW) is typically 100–150 °C below the classification temperature. Products made of polycrystalline wool can generally be used up to classification temperature.
Wool is an ordered accumulation of fibres of varying length and diameter. HTMW fulfills this definition and is therefore covered by the term wool. Amorphous AES and ASW are produced by melting the raw materials in a melting pot by means of electrical resistance melting. The jet of melt discharged from the pot is accelerated in a blowing or spinning process and pulled into fibres with different length / diameter ratios, and then formed into wool.