This specification defines fibrous glass materials used as acoustic-absorbing and thermal insulation media primarily used in automotive exhaust applications. The specification includes properties, both chemical and physical, required for moderate-, intermediate-, and high-temperature applications in exhaust systems.

Material Description. This specification describes three (3) types of fibrous glass materials typically used in silencer components of exhaust systems. The materials are classified as Type 1 for moderate-temperature applications, Type 2 for high-temperature applications and Type 3 for intermediate-temperature applications. These materials are utilized in environments where they will be exposed to hot exhaust gases, but the primary flow of the exhaust gasses is not normally through the mass of glass fibers. The fibers provide a mechanism for the dissipation of acoustic energy as well as providing thermal insulation around the path of the exhaust gases.

Material Identification

• Type 1, or moderate-temperature applications, are those applications where the fibrous material itself will achieve continuous operating temperatures of 730 °C or intermittent temperatures as high as 825 °C for up to 2 h. Thus, this material should be suitable for virtually all applications toward the rear of the exhaust system and many applications near the catalytic converter, either alone or in combination with a high-temperature material adjacent to the perforated tube.

• Type 2, or high temperature applications, are those applications where the fibrous material itself will achieve continuous operating temperatures of 825 °C or intermittent temperatures as high as 900 °C for up to 2 h. This material is suitable for virtually all applications toward the rear of the exhaust system and near the catalytic converter. 

• Type 3, or intermediate-temperature applications, are those applications where the fibrous material itself will achieve continuous operating temperatures of 810 °C or intermittent temperatures as high as 890 °C for up to 2 h. This material is suitable for virtually all applications toward the rear of the exhaust system and most applications near the catalytic converter.

Note: For many silencer applications in continuous operation, the glass temperature adjacent to the perforation tube is ≥ 50 °C below the exhaust gas temperature. For cyclic operations of a few minutes duration, this temperature differential is larger.

Typical Applications. These materials are typically used in exhaust systems where thermal insulation and/or acoustic attenuation are required. The choice of materials is primarily determined by the maximum operating temperature that the material will achieve.