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Related Reading

Plywood markings: how to read every stampHow the fire-retardant mark sits alongside the CE, formaldehyde and bond stamps on a single panel face.
Pressure treated plywoodHow chemical pressure-treatment works, covering FRT alongside the other treatment types.
Properties of plywoodWhere fire behaviour fits among plywood's strength, moisture and impact properties.
Plywood under a fireplace hearthIf the real question is heat near a hearth rather than a rated assembly, this answers it directly.
Film-faced plywood collectionVinawood's actual range — engineered for concrete forming and water resistance, not a fire product.

Quick Answers

Is plywood fire rated on its own?
No. Untreated plywood of any thickness or grade ignites and adds fuel like any wood. A fire rating comes from a chemical fire-retardant treatment plus a documented test result (such as ASTM E84 Class A) from a recognised lab — not from thickness, species, or brand. An 18mm sheet is not fire-rated because it is thick.
What is FRT plywood?
FRT means fire-retardant-treated plywood: plywood pressure-impregnated with fire-retardant chemicals so it chars slowly and resists surface flame spread. The char layer insulates the core and the treatment releases less flammable gas. It still burns — it buys time and limits flame spread, it is not fireproof.
Is fire-retardant plywood the same as fireproof?
No. No wood product is fireproof; "fireproof" is a misnomer to treat as a marketing red flag. "Fire-retardant" describes the treatment, "fire-rated" describes a tested class result, and "fire-resistant" is a loose umbrella term. Always ask which standard and class back the claim.
Can interior FRT plywood be used outdoors?
No. Interior FRT chemistry is hygroscopic and attracts moisture, which can corrode fasteners and, in some formulations at elevated temperature, reduce strength over time. Anywhere weather, condensation, or wash-down is in play, use exterior FRT, which uses leach-resistant chemistry.
Does fire-rated plywood cost more, and why?
Yes, meaningfully more. The premium pays for the pressure-treatment cycle, the kiln re-dry, the third-party fire test, and the certification paperwork that lets the panel be specified into a rated assembly. Exterior and structural FRT cost more again because of leach-resistant chemistry and adjusted-design-value documentation.