Intumescent means tumour forming. What on earth would you want one of those for in DIY?
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.
These hoods sit on downlighters fitted in ceilings. These fittings penetrate the plaster fire & smoke barrier, and the intumescent hood restores this layer of protection. In a fire the hood swells and blocks the hole.
May be used to add fire resistance where materials are joined.