Product Code: 16350. Consists of a high performance, self adhesive backed, PVC laminated intumescent material which has been designed to line the aperture of letterboxes in fire resistant doors. On exposure to a fire the liner will rapidly expand (intumesce) to seal the aperture and stop the spread of fire, smoke and hot gases through the door. The liner has been independently tested in accordance with BS476: Part 22: 1987 and the 50mm can provide in excess of 1 hour fire resistance, 30min 44mm.