The flame test is a simple practical method for identifying unknown plastics by the way a small piece burns: the flame colour, the smell, the amount of smoke, whether it drips and whether the material self-extinguishes. It gives a good indication but is never fully conclusive — when in doubt, combine it with other clues such as density (does it float on water?).
Characteristics by plastic
- Polyethylene (PE) and polypropylene (PP) — burn readily with a blue flame and yellow tip, drip, and smell of candle wax/paraffin. PE and PP float on water
- Polystyrene (PS) — yellow, heavily sooting flame with thick black smoke and a sweet gas/styrene smell
- PVC — hard to ignite and self-extinguishes outside the flame, flame with a green edge, sharp acrid smell (hydrochloric acid). Caution: the fumes are toxic
- Acrylic (PMMA, Perspex) — burns with a crackling, bright flame and a fruity, sweet smell
- Polyamide (PA, nylon) — drips and smells of burnt hair or celery
Application and safety
The flame test is used to sort offcuts, old pipes or profiles for repair or recycling. Always work safely:
- Take only a small piece and work in a well-ventilated area
- Avoid inhaling smoke — especially with PVC (hydrochloric acid) and PS
- Keep a means of extinguishing to hand and work over a non-combustible surface
Use the test as a first indication; for certain identification a laboratory analysis is needed.
Related terms
- ABS
- Acrylic
- EPDM
- PS
- PIR
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