What are the fire and smoke requirements for aerospace sandwich panels?

Compoform · 19 Sep 2026

Aerospace sandwich panels must meet strict fire and smoke standards set by aviation authorities, primarily the FAA in the United States and EASA in Europe. These regulations govern how quickly a material ignites, how far flames spread, and how much smoke a panel produces during combustion. The specific requirements depend on where in the aircraft the panel is installed and what structural role it plays.

This article covers the broader aerospace sandwich panel market. Compoform’s range is focused on PP honeycomb and PET foam cores for commercial vehicles and scaffolding — not aerospace interiors. The information below is provided as general technical context for engineers and procurement teams researching fire compliance across composite panel applications.

Which regulatory standards govern fire and smoke testing for aerospace panels?

The primary regulatory framework for aerospace sandwich panel fire and smoke performance is FAR Part 25 (Federal Aviation Regulations, Subpart F) in the United States and its European equivalent, CS-25, administered by EASA. Both frameworks require materials used in aircraft interiors to pass specific flammability and smoke tests before they can be certified for use. Compliance is not optional — uncertified materials cannot be installed in commercial aircraft.

Within these frameworks, the key testing appendix is FAR 25 Appendix F, which defines the test methods for vertical and horizontal flame propagation, heat release, smoke density, and toxic gas emissions. The standard is divided into multiple parts, each targeting a different fire scenario or material type. For sandwich panels specifically, Part IV (heat release) and Part V (smoke density) are the most demanding requirements.

In Europe, EN 45545 applies to railway rolling stock rather than aircraft, so it is not the governing standard for aerospace panels. However, engineers familiar with EN 13501-1 fire classifications used in construction and transport will find that aerospace standards are considerably more stringent — both in test conditions and in the limits applied to smoke production.

What fire tests do aerospace sandwich panels have to pass?

Aerospace sandwich panels must pass a combination of fire tests depending on their location and function within the aircraft. The most commonly required tests include vertical flame propagation (60-second Bunsen burner test), horizontal flame propagation, heat release rate measurement, and smoke density testing. Each test evaluates a different aspect of fire behaviour, and a panel must pass all applicable tests to receive certification.

Vertical and horizontal flame tests

The vertical flame test (FAR 25 Appendix F, Part I) exposes a panel sample to a direct flame for 60 seconds and measures how far the flame travels up the sample after the burner is removed. The burn length must not exceed 152 mm (6 inches), and the flame must self-extinguish within 15 seconds. The horizontal flame test applies similar logic but evaluates materials mounted in a horizontal orientation, which is relevant for ceiling and overhead panels.

Heat release rate testing

For larger panels and wall linings, FAR 25 Appendix F, Part IV requires heat release rate (HRR) testing using an Ohio State University (OSU) calorimeter. The panel must not exceed a peak heat release rate of 65 kW/m² and a total heat release of 65 kW·min/m² over the first two minutes of exposure. These limits are designed to prevent a fire from growing rapidly enough to block passenger evacuation routes.

How is smoke density measured and what are the limits?

Smoke density for aerospace panels is measured using the NBS smoke chamber test (ASTM E662), which quantifies how much light a smoke cloud absorbs during flaming and non-flaming combustion. The result is expressed as a specific optical density (Ds). FAR 25 Appendix F, Part V sets the limit at a maximum Ds of 200 at four minutes under both flaming and non-flaming conditions.

The NBS smoke chamber test places a panel sample inside a sealed chamber and exposes it to a radiant heat source. A photometer beam measures how much light passes through the accumulated smoke. A Ds value of 200 means the smoke is dense enough to reduce visibility significantly — so the regulatory limit is set to ensure that smoke levels remain below the threshold at which passengers would struggle to locate exits.

Some aircraft programs and airline customers impose tighter internal limits than the regulatory minimum, particularly for business class and first class cabin panels where aesthetics and occupant comfort are higher priorities. In practice, material suppliers targeting aerospace applications often aim for Ds values well below 200 to provide margin against test variability and to satisfy airline-specific requirements.

How does core and skin material choice affect fire performance?

The core and skin materials in a sandwich panel have a direct and significant effect on fire and smoke performance. Thermoset skins — such as phenolic or modified epoxy laminates — generally outperform thermoplastic skins in aerospace fire tests because phenolic resins char rather than melt, limiting flame spread and producing less smoke. Core material choice affects heat release rate, structural integrity under fire exposure, and the volume of combustion gases produced.

Phenolic skins are the most widely used facing material in certified aerospace interior panels because they meet heat release and smoke density limits with relatively straightforward formulations. Epoxy skins can meet the requirements but typically need flame-retardant additives, which can affect mechanical properties and add cost.

For core materials, Nomex honeycomb (an aramid fibre paper impregnated with phenolic resin) is the aerospace industry standard. It combines very low areal weight with excellent fire resistance and structural stability at elevated temperatures. Aluminium honeycomb cores are also used where fire performance requirements are less demanding, but they conduct heat more readily, which can be a disadvantage in certain fire scenarios.

Thermoplastic cores — including polypropylene honeycomb — perform well in transport and construction panel applications and can achieve classifications such as Bfl-S1 under EN 13501-1, which indicates limited flame spread and very low smoke production for flooring applications. However, thermoplastic materials generally do not meet the more demanding heat release and smoke density limits required for aircraft interior certification without significant modification or the addition of flame-retardant treatments.

What’s the difference between aircraft interior zones and their fire requirements?

Aircraft interiors are divided into zones based on passenger access, evacuation criticality, and proximity to ignition sources. Each zone carries different fire performance requirements. The most stringent requirements apply to cabin wall panels, ceiling panels, and overhead stowage compartments — areas where a fire could directly threaten passengers. Cargo compartment liners, galley structures, and lavatory panels each have their own specific test requirements under FAR 25.

Cabin sidewall and ceiling panels must pass heat release rate testing (OSU calorimeter) in addition to the standard flame and smoke tests. Cargo compartment liners face different requirements focused on containing a fire rather than preventing ignition — they must resist burn-through for a defined period to give the crew time to respond. Floor panels in passenger cabins must meet flame propagation limits but are not always subject to the same heat release requirements as wall panels.

Lavatory compartments are treated as a special case because they are enclosed, unmonitored spaces where a fire could develop undetected. FAR 25.853(d) requires lavatories to have built-in fire suppression systems, and all materials used inside them must meet the most stringent flammability classifications. This zone-based approach means that a panel configuration approved for one location in the aircraft cannot automatically be used in another without re-evaluation.

Can thermoplastic sandwich panels meet aerospace fire and smoke standards?

Standard thermoplastic sandwich panels — using PP or PET cores with glass-fibre reinforced thermoplastic skins — do not typically meet aerospace fire and smoke certification requirements in their base configuration. The heat release rates and smoke density values produced by unmodified thermoplastic materials generally exceed FAR 25 Appendix F limits. However, with flame-retardant additives, modified resin systems, or intumescent coatings, some thermoplastic formulations can be engineered to approach or meet specific aerospace requirements.

The practical challenge is that flame-retardant additives often affect mechanical properties, recyclability, and processing behaviour. For applications where aerospace certification is genuinely required, phenolic-based systems remain the dominant choice because they achieve compliance more reliably and with less compromise to structural performance.

Where thermoplastic sandwich panels excel is in adjacent transport sectors — truck bodies, trailers, buses, and rail vehicles — where fire standards are meaningful but less demanding than aerospace. In these markets, classifications such as EN 13501-1 Bfl-S1 (for flooring) or EN 45545 (for rail) are achievable with well-engineered thermoplastic panel constructions, and the weight, recyclability, and total cost of ownership advantages of thermoplastic materials are fully realized.

How Compoform Supports Fire-Compliant Panel Specification

We design and manufacture thermoplastic sandwich panels for commercial vehicles, trailers, and scaffolding — not aerospace interiors. Our panels are engineered and tested against European standards relevant to those markets, including EN 13501-1 for fire classification. Our QuikDeck floor panels, for example, carry a Bfl-S1 classification — combustible but with limited flame spread and very low smoke production — verified through EN ISO 11925-2 and EN ISO 9239-1 testing.

If you are specifying panels for a transport or industrial application where fire performance is a compliance requirement, here is how we support that process:

Panel configuration review: We assess your application, load requirements, and fire classification needs before recommending a core and skin combination.
Test documentation: We provide technical data sheets with fire classification data referenced to the specific test standards used — not generic claims.
Custom dimensions: Panels are produced to your exact dimensions, up to 13,500 mm × 2,950 mm, so you are not adapting a standard sheet to a non-standard application.
Application engineering: We review your assembly design, flag integration issues before production starts, and support you through the first production run.

For truck body floors and trailer decking where fire compliance, weight reduction, and long service life all matter, we act as an engineering partner from specification through to delivery. Contact our team to discuss panel requirements and we will review your application in detail before making any recommendations.