PBT
An engineering thermoplastic polyester
Typical values for the temper in the title
PBT is a semi-crystalline polyester (melting point about 223 °C) that crystallizes fast and is therefore easy to injection mold. It absorbs little water, is dimensionally stable, resistant to oils and many solvents, and has good electrical insulation properties.
It is used mainly for connectors and electrical components, automotive parts (sensors, housings), keyboards and appliance parts. It is usually used glass filled.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | 55 MPa | |
| Elongation A | 50% | |
| Modulus of elasticity E | 2.5 GPa | |
| Density ρ | 1.31 g/cm³ | |
| Rockwell hardness | M68 | |
| Machinability | 60% | relative rating in the site database |
Structure and family
| Feature | Value | Meaning |
|---|---|---|
| Type | semi-crystalline thermoplastic polyester | stability and insulation |
| Tm melting | about 223 °C | |
| Water absorption | low | dimensional stability |
Typical values per producer data sheets.
Grades and versions
In engineering polymers, the choice is between an unfilled grade, filled grades (glass or carbon fiber) and special grades (bearing, medical, food). Filler strongly changes strength, stiffness and expansion.
| Version | Properties | When to choose it |
|---|---|---|
| Unfilled | ductile | general parts |
| Glass-fiber filled (GF30) | strong and stiff | connectors and automotive parts |
| Flame retardant | UL 94 V-0 in suitable grades | electrical components |
Applications
- Connectors and electrical components
- Automotive sensors and housings
- Keyboards
- Appliance parts
- Handles
Fabrication
Hydrolysis
In hot water and steam over time PBT degrades (hydrolysis). For hot-water use there are special grades.
Machining
Use very sharp tools, a feed that does not overheat the material, and good support (the material is flexible and deforms under clamping). For precision parts, stress-relief annealing before final machining is sometimes performed.
Joining
Ultrasonic and laser welding.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| PA66 (Nylon 66) | 70-85 MPa | Ultrasonic | PA66: heat resistant, absorbs water · material page |
| POM (Acetal) | 70 MPa | Ultrasonic | POM: low friction, mechanical · material page |
| PPS | 165 MPa | Ultrasonic | PPS: chemical and heat resistant, expensive · material page |
Common mistakes
Using standard PBT in hot water long term
Hydrolysis degrades properties.
Using an unfilled grade for a structural part
Strength and stiffness are low.
Insufficient drying before molding
Water in the material causes hydrolysis during melting.
Equivalents, standards and supply
| ASTM | D5927 |
|---|---|
| Standards | ASTM D5927 |
| Forms | injection |
| Producers | BASF Ultradur · DuPont Crastin · Celanese Celanex |
Learn more
Values are typical for an unfilled grade (unless stated otherwise) and for comparison only. In polymers, properties depend on grade, filler, temperature, moisture and load duration. For design, rely on the producer data sheet for the specific grade. Sources: ASTM classification standards (D8033, D5205, D5204, D6394, D4067 and others), producer data sheets, and the METAL HUB materials database.
Updated: October 31, 2026