PBT and PET are the electrical industry's default polyesters. Glass-filled grades hold heat to 200 °C, resist tracking, and keep their dimensions in humid enclosures — which is why connectors, coil formers, switch housings and sensor bodies are so often moulded in them. PBT crystallises faster and is easier to process; PET is tougher and cheaper where the geometry allows a hotter tool.
Typical values for standard moulding grades. Exact figures depend on the specific compound or grade — confirm against your drawing before quoting.
Key properties
| Proprietà | Typical value |
|---|---|
| Densità | 1.30 – 1.40 g/cm³ (unfilled) |
| Tensile strength | 50 – 60 MPa unfilled / 120 – 150 MPa GF30 |
| Flexural modulus | 2.4 – 2.8 GPa unfilled |
| HDT at 1.8 MPa | 150 – 200 °C (GF30) |
| Mould shrinkage | 0.4 – 2.0 % depending on fill |
| Water absorption (24 h) | 0.1 – 0.4 % |
Values are typical for unfilled moulding grades at 23 °C unless stated. Glass-filled and specialty grades differ.
Typical applications
- Electrical connectors and terminal blocks
- Coil formers and bobbins
- Automotive sensor and actuator housings
- Switch bodies and relay components
- Pump housings and fluid-handling parts
Processing notes
- Dry 4 h at 120 °C. Polyester hydrolyses readily; wet resin loses molecular weight and the part turns brittle.
- PBT: melt 240 – 270 °C, mould 60 – 90 °C. PET needs a hotter mould, 100 – 140 °C, to crystallise properly.
- Glass-filled grades warp anisotropically. Gate position and fibre orientation decide whether a flat connector stays flat.
- Weld lines in glass-filled polyester are weak. Keep structural loads away from weld-line locations or specify a flow leader.
Frequently asked questions
PBT or PET for a connector?
PBT for most connectors — faster cycle, more forgiving process window, better dimensional consistency. PET where the part needs higher toughness or the tool can run hot enough to crystallise it properly.
Do you supply UL yellow-card documentation?
Yes, for the specific grade used. Send us the flammability and temperature rating you need and we will confirm the resin family before quoting, because the UL file number attaches to the grade, not the moulder.
Related materials
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Send us your PBT & PET drawing
Upload a 3D model or a 2D drawing and we will come back with a DFM review, a tooling cost and a piece price — usually within two working days.
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