PET
A dimensionally stable engineering polyester
Typical values for the temper in the title
PET in its engineering grade (semi-crystalline, Ertalyte or PET-P) is an excellent engineering plastic for precision mechanical parts: very dimensionally stable, absorbs very little water, stiff and wear resistant, with low friction. Its melting point is about 255 °C.
Compared with POM and polyamides it is more dimensionally and thermally stable, so it is used for precision parts, wheels and guides, valves and food-contact parts. Drawbacks: less tough under impact, and sensitive to hot water over time (hydrolysis).
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Density ρ | 1.39 g/cm³ | |
| Max continuous service temperature | ≈100–110°C | |
| Machinability | 80% | relative rating in the site database |
Structure and family
| Feature | Value | Meaning |
|---|---|---|
| Family | semi-crystalline polyester | |
| Tm | about 255 °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 PET-P | stable, wear resistant | precision parts |
| PET with solid lubricant | lower friction | bearings and guides |
Applications
- Precision mechanical parts
- Wheels and guides
- Valves
- Food-contact parts
- Sliding bushings
Fabrication
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.
Thermal expansion
The expansion coefficient of an unfilled polymer is several times that of a metal. In a precision part or an assembly with metal, design clearances accordingly.
Hydrolysis
Hot water (above about 60 °C) over time degrades the polyester.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| POM (Acetal) | 70 MPa | Ultrasonic | POM: tougher under impact, less stable · material page |
| PBT | 55 MPa | Ultrasonic | PBT: a polyester for injection molding · material page |
| PA66 (Nylon 66) | 70-85 MPa | Ultrasonic | PA66: absorbs water, changes dimensions · material page |
Common mistakes
Using it in hot water long term
It degrades by hydrolysis.
Choosing it for an impact part
POM is tougher.
Confusing it with bottle PET
Engineering PET is semi-crystalline and has different properties.
Equivalents, standards and supply
| ISO | PET |
|---|---|
| ASTM | D5927 |
| Standards | ASTM D5927 |
| Forms | sheet · rod · pellets |
| Producers | Mitsubishi (Ertalyte) · DSM (Arnite A) |
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