Friable means that a material is able to be reduced to a powder by hand pressure. Asbestos-containing materials that are friable have a much greater tendency to release fibers into the air. Conversely, non-friable asbestos-containing materials do not easily release their fibers into the air. Non-friable materials must be mechanically impacted to release fibers. Asbestos-containing floors, mastics, and siding are considered non-friable materials.