How do reaction to fire, non-combustible and fire resistance differ?

6 min read · Written by our team · Updated 26 Sept 2026

A small red flame from a burner on a bench beside three material sample blocks, with a section of a wall assembly standing behind them.

In short

These three terms answer different questions. Reaction to fire describes how much a *material* contributes to a fire starting and spreading in its early stage. Non-combustible is the level at which a material contributes almost no fuel in a standard test. Fire resistance describes how long a *complete wall, floor, door or opening seal* holds back fire in a test. A fire-resistance rating therefore belongs to a tested system, not to any single insulation slab — and none of the three is a "service temperature".

1Tests the material itself: how easily it ignites, how far flame spreads, smoke and burning droplets — then classifies it, for example under EN 13501-1. 'Non-combustible' is a result of this kind of test
2Smoke and droplets are part of the classification
3Tests the complete wall, floor or fire-stopping system on a furnace, built as it will be installed
4The result is how long it keeps meeting the criteria (for example 60 or 120 minutes) — it belongs to that system, not to one material

Comparison table

	Reaction to fire	Non-combustible	Fire resistance
---	---	---	---
Question answered	Does the material ignite easily, spread flame over its surface, give off much smoke?	Is the material fuel at all?	How long does a building element hold back fire?
What is tested	Material or product (including facings)	Material	Complete system, e.g. wall, floor, door, fire-stopping seal
Result reported	Class such as A1, A2, B…F, or a flame-spread index	Pass / fail, or class A1	Time in minutes, e.g. 60, 120, against set criteria
Example standard names	EN 13501-1, BS 476 Part 6 / Part 7, ASTM E84	EN ISO 1182, BS 476 Part 4	ISO 834, ASTM E119, BS 476 Parts 20–22, EN 13501-2
Interchangeable?	No	No	No

Reaction to fire

This looks at how far a material contributes to the start and early spread of a fire: whether it ignites easily, how much heat it releases, how fast flame spreads over its surface and whether it produces smoke or flaming droplets.

EN 13501-1 (Europe) classifies A1, A2, B, C, D, E, F, with sub-classes for smoke (s) and flaming droplets (d)
ASTM E84 (USA) reports a Flame Spread Index and Smoke Developed Index; for example, the SCG PCI documents report results to ASTM E84
BS 476 Part 6 / Part 7 (UK) test fire propagation and surface spread of flame

Facings such as foil or fabric affect the result; check the result for the faced product itself.

Non-combustible

This is the top level of reaction to fire. A material sample is placed in a hot furnace and checked for temperature rise, mass loss and flaming beyond set limits.

EN ISO 1182 is the main test for class A1 and is used with other tests for A2
BS 476 Part 4 is the British non-combustibility test for materials

Many stone-wool products reach this level. For example, ROCKWOOL ProRox WM states A1 to EN 13501-1, and ROCKWOOL Rocksafe Plus states non-combustible to BS 476 Part 4 — but "non-combustible" still does not tell you how many minutes a wall or opening will hold back fire.

Fire resistance

A complete building element is tested in a large furnace heated along a standard time-temperature curve (such as ISO 834 or ASTM E119) to see how long it meets the criteria. The main criteria in EN 13501-2 are:

R — load-bearing capacity: the structure does not collapse or deflect beyond limits
E — integrity: no flames or hot gases pass through to the other side
I — insulation: the temperature on the unexposed side stays within limits

Results are given as time, e.g. EI 120 means the E and I criteria were met for 120 minutes in the test. The result applies only to the configuration tested — thickness, density, compression, fixing, surrounding construction and opening size all matter.

Example: ROCKWOOL reports a fire-resistance result to BS 476 Part 20 for a tested installation of Rocksafe Plus; it is not a property of the stone-wool slab alone. See stone wool in passive fire protection.

Don't conclude this

"This insulation is non-combustible, so it gives 2 hours' fire resistance" — wrong: non-combustibility is a material property; fire-resistance time belongs to a tested system
"Stone wool melts above 1,000 °C, so it can be used on a 1,000 °C pipe" — wrong; see service temperature
"It passed ASTM E84, so it is a fire-rated material" — ASTM E84 is a surface flame-spread test, not a fire-resistance rating
"Fireproof" or "fire-resistant" in advertising can mean different things; always ask which standard it was tested to, and on which product or system

How to use this

Ask the seller whether a quoted figure is a material result or a system result, and ask for the test report or classification report
Fire requirements for a building depend on building-control law, building type and the local authority; they should be set by the designer or a fire-safety engineer
Fire-rated systems must be installed to the tested details by qualified installers
Several BS 476 parts are being replaced by EN standards in the UK; older documents may still cite BS 476

Sources

EN 13501-1 — Fire classification of construction products and building elements: reaction to fire tests
EN 13501-2 — Fire classification: fire resistance tests (R / E / I criteria)
EN ISO 1182 — Reaction to fire tests for products: Non-combustibility test
BS 476 Parts 4, 6, 7, 20, 21, 22 — Fire tests on building materials and structures
BSI — The changing status of the BS 476 standard series
ISO 834 and ASTM E119 — Fire resistance tests (standard time-temperature curve)
ASTM E84 — Surface Burning Characteristics of Building Materials
Scottish Government — Building standards technical handbook, Annex 2.E Reaction to fire
ROCKWOOL Asia — Fire resistance (Fire resilience)
ROCKWOOL — Rocksafe Plus Data Sheet; ProRox WM Product Data Sheets
SCG — SCG Insulation for Industrial : Pipe (PCI) catalogue