Mann McGowan - Interdens® A4 Sheets for Ironmongery ProtectionHinges, latches, locks, pivots and closers on timber based fire resisting doors are often forgotten and can seriously undermine the fire integrity of the door set. Interdens is a high performance intumescent material that insulates the timber, slowing down the charring process and providing fire protection from 30 minutes to over an hour in some tests. Sold in packs of 5, A4 sheets can be cut to suit hinge pads, lock kits and closers.