Icynene does not propagate flame but it can’t be classed as non-flammable because if there is something next to it that is on fire, it will burn.
For Icynene to continue to burn on its own it needs an oxygen index of 23%, but there’s only 20.8% in the atmosphere.
Unlike regular insulation board, which does burn when exposed at joints or where the foil has been damaged, Icynene is full of air, not gas. It’s the gas that supports the flame in insulation boards causing them to burn.
In a habitable room, Icynene should always be covered with plasterboard or other resistant board as per our BBA Certification.
If you have a minute there’s a useful video showing what happens when you try to burn Icynene.