Intumescent Letterbox Assemblies 30 min's Fire Protection. BS EN 1935. Smokeproof. Comes with a 10 year mechanical guarantee and is Fire door rated. A stylish ABS framed, adjustable telescopic sleeved letterbox, with metal flaps and fitted with a high performance intumescent liner. In the event of fire the intumescent liner expands rapidly and seals off the letterbox opening, preventing the spread of fire and smoke whilst maintaining the integrity of the fire door. An all-in-one letter plate solution for your front door. This letterbox assembly has an identical appearance from inside or outside the door hence no need for an additional internal letter tidy. Supplied in two parts, an aperture is created in the door and the two parts locate together forming a tunnel effect. Extending inner sleeves allows fitment to a variety of door thickness. To suit doors 40mm - 80mm thick. Fully sealed front plate. Fitted with brush pile draught excluders. Available in a variety of finishes. Suitable for all domestic, commercial and industrial use.