Cfl-s1 vs Bfl-s1 — What's the Difference and When Do You Need the Higher Class?

“Cfl-s1” and “Bfl-s1” both look reassuring on a datasheet, but they are not the same level of protection. This guide explains what separates them, when the higher class is worth specifying, and why a portable mat’s class has to come from a named test house — not a generic claim.

What’s the difference between Cfl-s1 and Bfl-s1?

Both are reaction-to-fire classes for floor coverings under EN 13501-1, and both carry the lowest-smoke “s1” suffix. The difference is the letter: Bfl performs better than Cfl in the standard radiant-panel test, so a Bfl-s1 material resists ignition and flame spread to a higher documented threshold than a Cfl-s1 one. Neither is “fireproof” — they describe tested behaviour, not a guarantee.

The “fl” subscript means the class applies specifically to flooring. As covered in our guide to fire classification for flooring under EN 13501, floor coverings are tested and labelled on a dedicated scale, separate from wall and ceiling products.

What does the flooring class hierarchy A1fl to Ffl mean?

EN 13501-1 ranks floor coverings from A1fl (best, effectively non-combustible) down through A2fl, Bfl, Cfl, Dfl and Efl, to Ffl (no performance determined). A smoke sub-class is added — and for floorings only s1 (lower smoke) or s2 exist; there is no s3 for floors. So a full label reads like Bfl-s1 or Cfl-s1. (Measurlabs)

For the combustible classes, the testing is twofold: Bfl, Cfl and Dfl all require both the EN ISO 9239-1 radiant-panel test (for critical heat flux and smoke) and the EN ISO 11925-2 single-flame ignitability test. A product passing only ignitability drops to Efl, and Ffl means it failed or was not assessed. So both Cfl and Bfl have already cleared the small-flame test — the radiant-panel result is what divides them.

What actually separates Cfl from Bfl?

The dividing measurement is critical heat flux (CHF) from the EN ISO 9239-1 radiant-panel test — the lowest radiant heat level at which flame stops spreading across the specimen. A higher CHF means the floor resists flame spread under stronger heat. Bfl demands a higher CHF threshold than Cfl, which is the whole reason Bfl ranks above it.

In that test, a horizontal floor sample sits under a gas radiant panel inclined at 30 degrees, producing a heat-flux gradient from roughly 10.9 kW/m² down to about 1.1 kW/m² across its length. (RISE) The indicative CHF thresholds are:

Flooring class	Indicative CHF threshold	Smoke options	Relative ranking
A2fl / Bfl	≥ 8.0 kW/m²	s1 or s2	Higher resistance
Cfl	≥ 4.5 kW/m²	s1 or s2	Market default
Dfl	≥ 3.0 kW/m²	s1 or s2	Lower

Those CHF figures are indicative / medium-confidence (Measurlabs) — useful for understanding the gap, but verify the exact pass criteria against the primary BSI/CEN text of EN 13501-1 before writing them into a specification. The “s1” smoke suffix is graded separately from the letter, so two products can share s1 yet sit at different CHF thresholds.

When is the higher Bfl-s1 class worth specifying for hot work?

Specify Bfl-s1 over Cfl-s1 when the floor sits closer to ignition risk: heavy spatter and slag from MIG/MAG or arc gouging, a continuous welding bay rather than occasional repairs, combustible sub-floors nearby, or where a client or insurer asks for the higher class. For lighter, intermittent work on a sound floor, a documented Cfl-s1 may be proportionate. Match the class to the actual process, not the worst-sounding label.

A higher fire class is necessary but never sufficient. The mat still has to take direct spatter, resist mechanical damage and — if welders stand on it — offer anti-fatigue comfort. See our guide to specifying welding bay matting and the difference between fireproof and fire-resistant matting. Whatever class you choose, matting supports — it does not replace — a hot work permit, fire watch and risk assessment.

Why does the class have to come from a named test-house datasheet?

A flooring fire class is only meaningful if it traces to a specific tested product, backing and thickness — so a portable mat’s Cfl-s1 or Bfl-s1 claim must come from a named test-house classification report, not be asserted generically for “rubber” or a product family. Standard organic rubber and PVC can actually scorch, smoulder or melt and behave as a fuel load. (The Fabricator)

Real-world examples show the range available. The market-default anti-fatigue welding mat, the COBA Diamond Tread, is tested to BS EN 13501-1 Cfl-s1 (COBA), while a modular tile product such as Workwell Link-Fire is stated by its manufacturer as Bfl-s1 (Workwell) — proof that the higher class is commercially available when a job warrants it.

When you compare options, ask for the classification report itself, confirmation it covers the product as supplied, and any site or insurer requirements. Browse fire-resistant matting and welding mats, or send us your process and we’ll help you specify the right class and request the supporting certificates.