Polybutylene terephthalate (PBT) is a thermoplastic engineering polymer that is used as an insulator in the electrical and electronics industries.

PBT resists solvents, shrinks very little during forming, is mechanically strong, is heat-resistant up to 150 °C (or 200 °C with glass-fibre reinforcement), and can be treated with flame retardants to make it noncombustible.

[4][5] Polybutylene terephthalate is used for housings in electrical engineering, but also in automotive construction as plug connectors and in households for example in showerheads or irons.

It is also found processed into toothbrush fibers and false eyelashes and is used in the keycaps[6][7] of some high-end computer keyboards because the texture is highly resistant to wear and the plastic is less vulnerable to ultraviolet degradation[8] and discoloration than the conventional ABS alternative.

Phosphorus-based flame retardant systems are used in these fire-safe polymers and are based on aluminium diethyl phosphinate and synergists.