Abstract
The flame-retardant properties of polyester fiber acoustic panels depend mainly on their formulation and manufacturing process. Ordinary PET sound acoustic boards are flammable. Flame-retardant PET sound-absorbing boards typically meet GB 8624-2012 Class B1, and often have additional classifications such as s1 and d0; some can meet ASTM E84 Class A or EN B-s1,d0. However, it is essentially still an organic material, not a non-combustible material. When purchasing, one should base decisions on authoritative test reports, consistency with the actual product, and the actual installation system, and strictly comply with the project’s fire safety regulations.
Debunking Misconceptions
Polyester Fiber Sound-Absorbing Boards Are Not “Non-Combustible Materials”
Polyester fiber sound-absorbing boards, also known as PET sound-absorbing boards, are made from polyester fibers, or PET. PET itself is a combustible thermoplastic polymer.
When exposed to fire, it generally undergoes the following processes:
- Shrinkage and melting;
- Thermal decomposition, producing combustible gases and soot;
- Continued combustion when exposed to an open flame; ordinary PET may continue to burn after the fire source is removed.
- Combustion may produce molten drippings that ignite materials below, a very dangerous point in a fire.
- Combustion products may include CO, CO₂, aldehydes, ketones, benzene compounds, and soot, and may also produce toxic gases.
Therefore, the core of flame retardancy is not “becoming non-combustible,” but rather:
- Reduced ignition susceptibility;
- Inhibition of flame spread;
- Self-extinguishing upon removal of flame;
- Reduced heat release;
- Reduced smoke density;
- Reduced molten dripping;
- Controlled smoke toxicity.
It must be emphasized that flame retardant does not equal non-combustible. Under sustained high temperatures and strong fire sources, polyester fiber sound-absorbing panels will still melt, decompose, and burn, producing smoke and toxic gases.
Pure PET substrates typically struggle to achieve true Class A non-combustibility.
How to interpret the rating
The combustion performance of Chinese building materials is mainly determined by GB 8624-2012, “Classification of Combustion Performance of Building Materials and Products.” See Table 1.
Table 1: Combustion Performance Ratings of Building Materials and Products
| Combustion Performance Rating | Name |
| A | Non-combustible materials (products) |
| B1 | Flame-retardant materials (products) |
| B2 | Combustible materials (products) |
| B3 | Flammable materials (products) |
In addition to the main rating, there are three additional categories of information:
- s1/s2/s3: Smoke production characteristics, with s1 producing the least smoke (optimal);
- d0/d1/d2: Combustion drips/particulate matter, with d0 producing no ignitable drips (optimal);
- t0/t1/t2: Smoke toxicity, with t0 having the lowest toxicity (optimal).
Examples of common testing markings for polyester fiber sound-absorbing panels in China:
- GB 8624 B₁ (B-s1,d0)
- GB 8624 B₁ (C-s1,d0)
Low-end products with poor flame retardancy can only achieve GB 8624 B₂ (D-s2,d2) or even B3 level.
Important Distinction (Key to Foreign Trade):
- US Standard ASTM E84 Class A ≠ GB 8624 Class A non-combustible. ASTM E84 only measures flame spread and smoke development index, evaluating only surface flame propagation; the material itself remains an organic combustible material, and they cannot be interchanged for acceptance.
- EU EN 13501-1, although using the same letter symbols as GB8624-2012 (B-s1,d0, C-s1,d0), has different test criteria and parameters, and cannot be directly substituted; it can only be used as a reference for roughly similar performance, and cannot replace test reports. EU testing for polyester fiber sound-absorbing panels often yields EN 13501-1 B-s1,d0 or C-s1,d0.
Typical Flame Retardant Performance of Polyester Fiber Sound-Absorbing Boards
Qualified B1-grade polyester fiber sound-absorbing boards typically exhibit the following characteristics:
- Difficult to ignite under small fire sources;
- Relatively quick self-extinguishing after removal of the fire source;
- Slow flame spread;
- Low peak heat release rate;
- Low smoke production, reaching s1;
- Minimal dripping, reaching d0;
- Low smoke toxicity, reaching t0/t1.
However, it must be emphasized that flame retardancy does not equal non-combustibility. Under sustained high temperatures and strong fire sources, it will still melt, decompose, and burn, producing smoke and toxic gases.
Common Flame Retardant Processes for Polyester Fiberboard
Common flame retardant methods for polyester fiber sound-absorbing boards include:
- Raw fiber flame retardancy: Flame retardants are added during the polyester polymerization or spinning stage, resulting in a longer-lasting effect;
- Impregnation flame retardancy: Finished polyester boards are impregnated or sprayed with flame retardant liquid. This method is low-cost, but its effectiveness may decrease with humidity, wiping, washing, and aging.
When purchasing, it is essential to clarify: Is it raw fiber flame retardant or impregnation flame retardant? Is it moisture-resistant?
Impregnation flame-retardant boards may fail after prolonged exposure to moisture. This is particularly important in projects such as kindergartens, hospitals, and underground spaces.
Key Procurement Points: 5 Things to Consider
1. Confirm the required fire rating.
Check design drawings, fire safety review opinions, and relevant local regulations to clarify the required fire rating for the intended use area.
If the regulations require Class A non-combustible, pure polyester fiber sound-absorbing panels usually do not meet this requirement, necessitating an upgrade to acoustic materials with higher fire resistance.
2. Clearly state the complete classification.
The procurement documents should specify:
- Standard: GB 8624-2012;
- Rating: e.g., B-s1,d0 or C-s1,d0;
- Additional classifications: s1, d0, t0/t1.
3. Verify the test report.
Check if the report has CMA/CNAS accreditation, whether it is currently valid, and whether its authenticity can be verified on the official website.
Key points to check:
- Sample name, model, thickness, density, color, and finish;
- Is it a bare sheet or a finished product with a finish and adhesive backing?
- Is it a commissioned inspection, type inspection, or batch inspection?
- Does the report match the actual product?
Ideally, seal the sample and request batch sampling or third-party re-inspection.
4. Focus on flame retardancy durability.
Clarify the flame retardant process, including its resistance to washing, moisture, aging, and disinfection/wiping.
Immersion flame retardancy is cheaper, but its durability is poor.
5. Smoke, toxicity, and dripping are key.
Polyester fibers melt and drip when burning, so pay special attention to:
- d0: No dripping;
- s1: Low smoke;
- t0/t1: Low toxicity.
This is especially important in public places such as underground spaces, evacuation routes, and enclosed spaces.