Pre-baked felt is composed of textile fibers (cotton) bonded with a phenolic or non-phenolic resin (epoxy or thermoplastic). It may optionally contain a flame retardant or expandable agent, which gives it high firmness, rigidity, and fire resistance that varies according to the composition specified by the customer.

Pre-cured felts are designed to be partially finished during production. The molding process then activates the resin and forms the rigid part. Due to their semi-finished state, the felts are flexible and require further curing.

Depending on the choice of resin, the felts will be molded hot (phenolic resin) or cold (epoxy resin, also called thermoplastic).

In the second case, the felt will undergo a heating cycle. Phenolic felts are generally chosen for their heat resistance. They are found in the engine compartment and around exhaust systems.