Burning a small sample of a synthetic fibre yarn is a handy way of identifying the material. Hold the specimen in a clean flame. While the specimen is in the flame, observe its reaction and the nature of the smoke. Remove the specimen from the flame and observe its reaction and smoke. Then extinguish the flame by blowing. After the specimen has cooled, observe the residue.
| Nylon 6 and 6.6 | Polyester | Polypropylene | Polyethylene | |
| In Flame | Melts and burns | Shrinks and Burns | Shrinks, curls, and melts | |
| White smoke | Blackish smoke | |||
| Yellowish melted falling drops | Melted falling drops | |||
| Removed from Flame | Stops burning | Continues to burn rapidly | Continues to burn slowly | |
| Small bead on end | Small black bead on end | |||
| Hot melted bead | Hot melted substance | Hot melted substance | ||
| Can be stretched into fine thread | Cannot be stretched | |||
| Residue | Yellowish bead | Blackish Bead | Brow/yellowish bead | Like paraffin wax |
| Hard round bead, Not crushable | No bead, Crushable | |||
| Smell of smoke | Celery-like Fishy odor | Oily sooty odor Faintly sweet, like sealing wax | Like burning asphalt orparaffin wax | Like burning paraffinwax |
| February 23, 2003 | ||||
The colour only applies to undyed fibre. Smell might be altered by agents in or on the fibre.
The sense of smell is subjective and should be used with reservation.
Other fibre characteristics may also aid in identification. Polypropylene and polyethylene float on water; nylon and polyester do not. Nylon and polyester are usually white. Polypropylene and polyethylene are sometimes dyed. Polypropylene and polyethylene fibres are usually, but not always, much thicker than nylon and polyester.
Appropriate cautions must be taken with flames and hot substances!
For critical applications, expert advice should be obtained.