Intumescent Materials

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Intumescent means tumour forming. What on earth would you want one of those for in DIY?

Intumescent Materials are used for fire protection. On exposure to fire, the items swell up to form a fire and smoke resisting foam that blocks fire spread for anything upto an hour.

Intumescent Products

Intumesent products generally contain melamine as the blowing agent, ie its the melamine that expands when hot.

Door seals

These are strips that go into grooves routed into the sides and top of a door. These are a common sight in large buildings.

They prevent fire spread from room to corridor, or vice versa, and protect occupants in other rooms from the smoke, which can be toxic.

Downlighter hoods

These hoods sit on downlighters fitted in ceilings. Downlighters penetrate the fire & smoke barrier, and the intumescent hood restores this layer of protection. In a fire the hood swells and blocks the hole.

DIYers have been known to use clay flowerpots as a cheaper (non-intumescent) alternative.

Its now more popular to use lights with built in hoods. These are heatsinked, reducing heat build up.


Flammable surfaces in need of fire protection where no visible bulk would be acceptable can be painted with intumescent paint. It isn't cheap.


Woodwork can be painted with clear intumescent varnish to create an invisible fire barrier.


May be used to add fire resistance where materials are joined.


Non setting intumescent putty fills gaps where pipes pass through walls. It allows pipe movement, and can be removed and reused if ever necessary.

Other options

Sometimes there are cheaper alternatives.


Oak is fire resistant, in a fire it forms a layer of fire resistant char, delaying consumption. This feature is occasionally made use of in building design, and is the reason oak was preferred for electrical wiring accessory backing plates long ago.


Brick & tile can also be used to create a fire barrier.

See Also