Flame-Retardant Plastics: Properties, Standards, and Material Options

What is Flame Retardancy?

Flame-retardant plastics resist ignition and can self-extinguish if exposed to fire. Unlike metals, plastics are organic and combustible, so flame resistance is an important factor in material selection.

For components used in high-temperature environments or near open flames, flame-retardant plastics reduce fire hazards and improve product safety. Flame resistance is typically measured using the UL94 standard or the Oxygen Index.

• UL94 Standard – Classifies materials into six grades (HB, V-2, V-1, V-0, 5V-B, 5V-A) based on their ability to self-extinguish. Grades V-2 and above have self-extinguishing properties, with higher grades extinguishing more quickly.

• Oxygen Index (JIS) – Indicates the minimum oxygen concentration required to sustain combustion. A higher index means better flame resistance.

Flammability Rating Criteria

HB (Horizontal Burning) Grade

The HB grade is determined by placing a specimen horizontally and exposing it to a 20 mm flame for 30 seconds. Burn rate after flame removal defines whether it meets HB standards:

• Thickness ≥ 3 mm: burn rate ≤ 40 mm/min

• Thickness < 3 mm: burn rate ≤ 75 mm/min

This ensures minimum flame-retardant performance for safe use in general applications.

Certification Criteria for V-0, V-1, V-2

Certification Criteria for 5V-A, 5V-B

Flame-Retardant Plastics (V-0 or Higher)

Most flame-retardant plastics are super engineering plastics, designed for high heat resistance and demanding applications.

PEEK

PEEK is a high-performance thermoplastic with the highest heat resistance and mechanical strength among thermoplastics. It has a continuous service temperature of 240–260 °C and can withstand continuous exposure to steam. PEEK also produces very little smoke and toxic gas when burned and exhibits low outgassing in a vacuum. Because it performs exceptionally across multiple properties, PEEK is more expensive than other thermoplastics.

PPS

PPS offers excellent heat resistance, dimensional stability, and mechanical strength. It has a continuous service temperature of approximately 220 °C and produces very little smoke when burned. With a glass transition temperature of 97 °C, PPS may deform under high temperatures and heavy loads, even below its continuous service temperature.

PTFE 

PTFE is a fluoropolymer with outstanding heat, chemical, and abrasion resistance. It has a continuous service temperature of 260 °C and maintains its mechanical strength at temperatures as low as –250 °C. Its molecular structure resists bonding with oxygen, making it flame-retardant, difficult to ignite, and resistant to flame propagation.

PVDF

PVDF is a versatile fluoropolymer with strong processability and weather resistance. It has a continuous service temperature of 140 °C and a stable dielectric constant. While its heat and chemical resistance are lower than PTFE, PVDF is widely used because of its mechanical strength and superior weather resistance compared with general-purpose resins.

PEI

PEI is a chemically resistant amorphous resin with excellent insulation properties. It has continuous service temperatures up to 170 °C without degradation and is resistant to steam and hot water. PEI also maintains stable dielectric performance across a wide frequency range.

PAI

PAI has the highest mechanical strength among unfilled plastics. It has a continuous service temperature of 250 °C and resists most chemicals and radiation. These properties make PAI widely used in electronics, aerospace components, and medical equipment.

PI

PI is an ultra-high-heat-resistant plastic with continuous service temperatures up to 300 °C. It can withstand intermittent temperatures up to 480 °C and retains its properties even at extremely low temperatures, down to –260 °C.

Slow-Burning Plastics (HB Grade)

These plastics meet minimum flame resistance but burn more slowly rather than self-extinguishing.

PMP

PMP is a high-molecular-weight hydrocarbon similar to polypropylene. It has a continuous service temperature of 115 °C and resists hydrolysis even in boiling water, making it suitable for steam sterilization. PMP also has strong resistance to acids and alkalis, though it is less resistant to certain organic solvents.

PBT

PBT is an engineering plastic with a continuous service temperature of 120–140 °C. It has low water absorption and thermal shrinkage, giving it excellent dimensional stability.

POM

POM is a versatile engineering plastic with strong mechanical strength, wear resistance, and chemical resistance. Its ease of machining and low cost make POM widely used in components across various industries.

ABS

ABS is a general-purpose plastic with high mechanical strength and low cost. It is suitable for a wide range of applications, from machine parts to consumer products. However, ABS has poor weather resistance and is not recommended for outdoor use.

Polycarbonate

Polycarbonate is a transparent resin with the highest impact resistance among plastics. It has a continuous service temperature of 120 °C and is commonly used for exterior parts, protective covers, and other applications requiring durability.

Acrylic

Acrylic (PMMA) is a transparent resin with light transmittance of about 93%, higher than glass. It has better impact resistance than glass, and when broken, shards are less likely to scatter. Acrylic also offers excellent weather resistance, making it suitable for outdoor use, though some discoloration may occur over time.

Paper Bakelite

Paper Bakelite is a laminated material that balances mechanical strength, heat resistance, and chemical resistance. It performs best under forces applied perpendicular to the laminate but may chip or crack under horizontal stress. Paper Bakelite is more affordable than cloth Bakelite.

Cloth Bakelite

Cloth Bakelite is a laminated material with strong mechanical strength, heat resistance, and chemical resistance. It is more expensive than paper Bakelite but provides superior durability.

Epoxy Glass

Epoxy glass is a laminated material made from glass fibers and epoxy resin. It has greater mechanical strength and heat resistance than Bakelite. However, epoxy glass is brittle, prone to chipping, and produces hazardous dust during machining, so few companies handle it.

MC Nylon

MC Nylon is a widely used general-purpose material with well-balanced properties and moderate cost. It has high water absorption, which can lead to dimensional changes due to moisture.

Nylon 6

Nylon 6 is a durable engineering plastic with excellent impact and chemical resistance. It absorbs water, which increases flexibility and improves impact strength. Nylon 6 also has self-lubricating properties, making it suitable for sliding components.

Step Up Your Project with Yumoto Electric

Yumoto Electric delivers high-quality components fast, worldwide. We provide precision machining for a wide range of engineering plastics, including PEEK, PPS, MC Nylon, and POM.

If you’re unsure about material selection or machining methods, we offer complimentary consultations to help optimize your design and production. For any questions, please feel free to contact us.