Where halogen-free laminates are asked for
Specifications for passenger rail and metro interiors, ships and some buildings often limit not only how a material burns but what its smoke contains. Halogenated flame retardants can release acidic, corrosive gases when they burn, so some of these specifications restrict or exclude them. A laminate that must be fire-retardant and halogen-free is the result.
What the specification must tell you
Questions for the project
- Which fire standard applies, and which classification or hazard level is required?
- Is halogen-free stated explicitly, or implied by a smoke-toxicity limit?
- What is the part, where is it installed, and which face is exposed?
- What laminate construction and thickness is planned, including gelcoat and any core?
- Who performs and pays for the fire testing?
The grades that fit
SPR 201 FR (HF) is the halogen-free grade of the orthophthalic SPR 201 family, listed for halogen-free FR laminates and marine composite components. The ISO Fire Retardant Resin is a halogen-free, ATH-filled isophthalic alternative with its own TDS. Where halogens are acceptable, the halogenated SPR 201 FR is also available.
Whichever laminating resin is chosen, the outer surface normally needs a fire-retardant gelcoat as well, because the gelcoat is the first layer a flame reaches.
Published typical values
The figures below come from each product’s own document. Note the difference in viscosity and specific gravity between the grades: they are not interchangeable in the workshop.
| Property | Halogen-Free Fire-Retardant Resin (SPR 201 FR (HF)) | ISO Fire Retardant Resin (SPR 301 FR) | Fire Retardant Resin (SPR 201 FR) |
|---|---|---|---|
| Chemistry | Orthophthalic unsaturated polyester, halogen-free fire-retardant | Unsaturated Polyester Resin (Fire Retardant Grade) | Not published |
| Appearance | White to light-yellow opaque liquid | White | White |
| Viscosity (typical) | 1,500–3,500 cPs at 25 °C | 400 cPs | 400 cPs |
| Gel time / pot life (typical) | 15–30 minutes at 25 °C | 5.5 minutes | 5.5 Minutes |
| Specific gravity / density (typical) | 1.25–1.45 | 1.18 g/cm³ | Not published |
| Source of values | 2026 catalogue; grade TDS | ISO Fire Retardant Resin TDS | Fire Retardant Resin TDS |
Typical values, reproduced from each product’s own published data. They describe the liquid resin at its reference condition, not a finished part, and are not guaranteed limits.
Working with a filled, opaque resin
Halogen-free fire-retardant resins commonly rely on mineral fillers. That makes them opaque and raises their viscosity and weight; SPR 201 FR (HF) is typically 1,500–3,500 cPs at 25 °C with specific gravity 1.25–1.45. Filled resins wet reinforcement more slowly, can hold air more readily and may settle in storage, so mixing, wet-out and consolidation all deserve attention in trials.
Proving the part
A fire classification belongs to a tested specimen of the finished construction. Plan for the gelcoat, laminating resin, reinforcement, thickness and any core to be fixed before the test panels are made, and for production to follow that construction. A resin change after testing can void the result.