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Myth or reality? “Does non-combustible insulation protect you from fire?"

Published on 21.07.2026 · Isoflect Insulation technical team

The guide to the truth about insulation

The myth: “Non-combustible insulation protects you from fire"

Sellers of stone wool turn a laboratory classification into a promise of personal safety. It is worth unpacking what the label actually says — and what happened in real buildings that had exactly this material in their walls.

What the label actually says

Three things the technical data sheet knows, but the advertising does not proclaim.

EN 13501-1 · Class A1

Reaction to fire, not protection

Euroclasses measure how much the material itself contributes to the development of a fire. A1 means that the material does not add extra fuel. Nothing more. It does not mean that it stops the fire, that it protects the structure or that it buys you time for evacuation.

EN 13501-2 · EI / REI

Fire resistance belongs to the wall, not to the bag

Fire resistance is a property of the building element — wall, floor slab, complete assembly — tested as a system. A bag of stone wool does not have “fire resistance". A correctly compartmented wall, with everything it contains, may have it.

The nuance in the data sheet

The fibre withstands, the binder does not

Basalt fibre itself withstands very high temperatures, but the boards also contain an organic binder (resins), which degrades thermally at temperatures far lower than the fibre. “Non-combustible" describes classification behaviour, not indestructibility.

What real fires show

Three documented cases — with official reports and press coverage — in which the building contained non-combustible mineral wool. And it still burned.

London · UK 2019

Richmond House, Worcester Park

A four-storey block insulated with non-combustible mineral wool, confirmed by the post-fire investigation, with external cladding of limited combustibility — “on paper", the perfect envelope. Completely destroyed; approximately 60 people evacuated at the last moment. The fire spread through the timber battens in the cavity, behind the non-combustible cladding.

The mineral wool fire barriers — installed precisely to stop the flames — were defective and, according to the official report, “made no contribution" to slowing the fire. One resident described the spread as almost instantaneous.
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