Asbestos mill board is a type of fire-resistant material that was historically used in various industrial applications due to its exceptional heat resistance and insulating properties. It was commonly composed of a mixture of asbestos fibers and a binder material. The asbestos fibers provided heat resistance and strength, while the binder held the fibers together.

Asbestos mill board was often used for gaskets, seals, and insulation in equipment that operated at high temperatures, such as boilers, furnaces, and steam pipes. Its ability to withstand intense heat and serve as an effective thermal barrier made it a popular choice in industries where heat containment and insulation were critical.