The FireBlocker system is an advanced fiber system located among the outer layers of the mattress and box spring, and contains no harmful chemicals. A precise blend of natural and synthetic fibers, FireBlocker isolates the impact of a fire and blocks its spread into the mattress. In fact, Serta mattresses with FireBlocker exceed existing and proposed, state and federal residential open-flame resistance standards. Three years in development, the FireBlocker system was tested at Underwriters Laboratories, and its results were UL-confirmed.