Foam acoustic panels are cheap and absorb high frequencies well, but standard polyurethane foam ignites easily and produces toxic smoke unless it is fire-retarded and tested. PET felt panels absorb comparably at similar thickness and are published at higher fire classes. Wood slat panels add a durable, architectural face. For commercial interiors, choose classified PET or wood-based products.
Key takeaways
- Absorption depends mainly on pore structure and depth, not on whether the absorber is foam or polyester fibre.
- NIST found that non-fire-retarded polyurethane foam on walls and ceiling drove the fatal spread of The Station nightclub fire in 2003.
- Laboratory work on flexible polyurethane foams shows carbon monoxide and hydrogen cyanide emissions that exceed permissible values.
- PET felt and wood slat panels are available with published fire classifications; always check the report for the exact build.
- Foam suits only small, low-risk rooms when it carries a valid fire classification; PET and slat suit commercial projects.
Last reviewed: October 2026 by the Linegrain specification team.
Do foam, PET felt and wood panels absorb sound differently?
Less than marketing suggests. Porous absorbers work by forcing air to move through a maze of small pores, where friction turns sound energy into heat. Professor Trevor Cox of the University of Salford explains in Sound On Sound that what counts is the size, shape and connectivity of the pores, not the material of the matrix, and that for a given depth mineral wool performs a little better than foam. Depth matters most: his rule of thumb is that a porous absorber needs to be at least a tenth of a wavelength thick, and spacing it off the wall can be as effective as making it thicker.
So a 25 mm open-cell foam tile and a 24 mm PET felt panel will both be good mid/high absorbers and weak bass absorbers. The published data bears this out for felt: the Autex Cube datasheet reports NRC 0.70 for 24 mm polyester panel direct-mounted and 0.80 with an air gap.
Wood slat panels are different in construction. The slats themselves reflect; sound passes through the gaps and is absorbed by the felt and any cavity behind. A University of Salford test of 12 mm slats (27 mm wide, 13 mm gaps) on a 10 mm felt panel, laid directly on a hard floor, measured practical absorption of 0.70 at 1 kHz and 1.00 at 2 kHz but only 0.05 at 125 Hz, rated αw 0.30, class D (Salford report 06352-6183). In practice slat panels are chosen for appearance and durability and then mounted over battens and insulation when more low-frequency absorption is needed. Our article do acoustic slat panels work? covers this in detail.
Why is acoustic foam a fire concern?
Flexible polyurethane foam is a fuel-rich, low-density material with a large exposed surface. Unless it is formulated and tested as fire-retarded, it can ignite from a small flame and spread fire quickly across a wall or ceiling.
The clearest public evidence comes from the US National Institute of Standards and Technology investigation of The Station nightclub fire in West Warwick, Rhode Island, in February 2003. NIST reports that pyrotechnics ignited polyurethane foam insulation lining the walls and ceiling of the stage platform. Smoke was visible in the exit doorways in a little more than one minute, flames broke through part of the roof in under five minutes, and 100 people died. NIST recommended that model codes forbid easily ignited materials, including non-fire-retarded flexible polyurethane foam, in new and existing nightclubs, and that sprinklers be required.
Smoke toxicity
Fire spread is only part of the risk. A 2023 study published in the journal Materials by Borucka and colleagues (Analysis of Flammability and Smoke Emission of Plastic Materials) tested four commercial flexible polyurethane foams and found that carbon monoxide and hydrogen cyanide emissions exceeded permissible values and posed a serious threat to life and health; hydrogen cyanide yields increased under poorly ventilated conditions. The authors also note that a standard cone calorimeter test of flammability does not capture smoke toxicity, which is a reason to look beyond a single headline fire figure.
None of this means every foam product is dangerous. Fire-retarded foams exist and some carry classifications. It does mean that foam bought without a classification report has no place on the walls or ceilings of a shop, restaurant, office, school or venue.
How do PET felt and wood slat panels perform in fire?
Both depend on the exact build, and both are available with published classifications. Autex, for example, lists its Cube polyester panel at ASTM E84 Class A, with flame spread 0, and at Euroclass B under BS EN 13501-1 for walls and ceilings, in the same datasheet cited above. For slat panels the result depends on the board (standard MDF or fire-retardant MDF), the veneer or laminate, any lacquer and the felt.
For the US market, interior finishes are graded under ASTM E84. As WoodWorks explains for the IBC, Class A is a flame spread index of 0–25, Class B 26–75 and Class C 76–200, each with a smoke-developed index no higher than 450. In the UK and EU the equivalent is a reaction-to-fire class under EN 13501-1, which also reports smoke (s1–s3) and flaming droplets (d0–d2). Our guide to acoustic panel fire ratings explains how to read those reports.
Linegrain supplies slat panels on E1 MDF as standard, with fire-retardant MDF on request (see the fire-rated acoustic slat panel), and shares fire and acoustic test reports for the specific build quoted.
Which lasts longer?
Lifespan is harder to put numbers on, and we have not found an independent study comparing service life across these materials, so the guidance below is qualitative.
- Open-cell foam is soft and easily dented or torn. Polyurethane foams can discolour with light exposure and may become brittle or crumble with age, especially near windows or heat sources.
- PET felt is a dense, homogeneous fibre board. It tolerates knocks, can be pinned into and does not have a face layer to peel. Heavy rubbing can roughen the surface, so manufacturers advise blotting spills rather than scrubbing.
- Wood slat panels present a hard, sealed timber or laminate face that resists everyday impacts and can be dusted or wiped. The felt backing sits behind the slats, protected from contact.
Comparison table
| Factor | Polyurethane foam tiles | PET felt panels | Wood slat on PET felt |
|---|---|---|---|
| Absorption character | Mid/high; depends on thickness | Mid/high; NRC rises with thickness and air gap | Strong at 1–2 kHz; low at 125 Hz direct-fixed; improves over a cavity |
| Fire behaviour | High ignition and spread risk unless fire-retarded and classified | Classified products published at ASTM E84 Class A and Euroclass B | Depends on board and finish; fire-retardant MDF option |
| Smoke | CO and HCN emissions documented in lab studies | Check smoke class (s1–s3) in the report | Check smoke class in the report |
| Durability | Low; tears, dents, discolours | Good; impact tolerant, pinnable | Very good; hard face |
| Appearance | Utility, studio look | Colour, grooves, prints, shapes | Architectural, natural timber or laminate |
| Typical use | Small private rooms, only with a valid fire classification | Offices, schools, screens, baffles | Hotels, restaurants, offices, residential feature walls |
Which material should you specify?
- Commercial, hospitality or public buildings: specify PET felt or slat-on-felt products with a classification report that covers the exact build and location. Explore PET felt acoustic panels and acoustic slat panels.
- Private home studio: foam can work if it carries a recognised fire classification, but felt or slat panels last longer and look better.
- Private-label product ranges: buyers increasingly ask for fire documentation up front, so build the range around materials you can document. See how we handle quality and testing.
FAQ
Is acoustic foam fire resistant?
Not by default. Standard flexible polyurethane foam ignites easily. Some foams are fire-retarded and classified, but you must see the classification report for the specific product and thickness.
Is PET felt better than foam for sound absorption?
At the same thickness and mounting they perform in a similar range, because absorption depends mainly on pore structure and depth. PET felt’s advantages are durability, appearance and the availability of published fire classifications.
Are wood slat panels safe for commercial use?
They can be, provided the build carries the reaction-to-fire class required for the location. Fire-retardant MDF and suitable finishes help; the test report must match the build supplied.
Can I test PET and slat samples before ordering?
Yes. Sample cost and shipping are quoted by our team depending on the items and quantity.
Replacing foam with documented PET felt or slat panels? Tell us the application and fire class you need and we will quote a build with matching test reports. Request a quote.