PBT Polyester (Ultradur): Fast-Cycling Electrical & Automotive Plastic
Published: 2026-06-02
Polybutylene terephthalate (PBT) is the fastest-cycling engineering thermoplastic, crystallizing rapidly at mold temperatures of only 40-80°C — cycle times are typically 20-40% shorter than equivalent PA66 parts. This fast crystallization is...
Polybutylene terephthalate (PBT) is the fastest-cycling engineering thermoplastic, crystallizing rapidly at mold temperatures of only 40-80°C — cycle times are typically 20-40% shorter than equivalent PA66 parts. This fast crystallization is PBT's defining processing advantage. Combined with low moisture absorption (0.08% at equilibrium vs 2.5-3.0% for PA66), PBT maintains dimensional stability in humid environments without the need for pre-drying. Key applications: automotive electrical connectors, relay housings, sensor bodies, and consumer electronics where fast cycle times drive part economics.
PBT's limitations: low HDT (65°C unfilled) limits high-temperature applications unless glass-reinforced (30GF raises HDT to 205°C). Notch sensitivity at low temperatures — avoid impact loading below 0°C. Poor resistance to hot water (>60°C) and strong alkalis — hydrolysis degrades the ester linkage. For hot water exposure, PPS or PSU are preferred alternatives. Glass-filled PBT (GF10-30%) is the standard for under-hood automotive connectors, combining fast cycle times with adequate thermal performance.
Technical Properties
| Density | 1.31 g/cm³ |
|---|---|
| Tensile Strength | 60 MPa |
| Melting Point | 223 °C |
| Shrinkage Rate | 1.5-2.2% |
| Flexural Modulus | 2.5 GPa |
| Hdt | 65 °C at 1.82 MPa |
Engineering Tool: Shrinkage & Cost Estimator
Calculate part weight, mold cavity dimensions accounting for shrinkage, and material cost — all locally in your browser.
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| Ultradur B4520 | |
| Crastin S600 | |
| Valox 325 |
Frequently Asked Questions
Why choose PBT over PA66 for connectors?
PBT cycles 20-40% faster (lower melt temp, faster crystallization), requires no pre-drying in most cases, and maintains dimensional stability across humidity changes. PA66 is stronger and has higher HDT, but absorbs 2.5-3% moisture which causes dimensional swelling and property reduction. For connectors, the dimensional stability advantage often outweighs the strength disadvantage.
Does PBT need to be dried before molding?
PBT is less hygroscopic than PA66 (0.08% equilibrium moisture vs 2.5%), but still benefits from drying at 120°C for 3 hours if the material has been exposed to ambient air for >4 hours. Hydrolysis at processing temperatures causes a characteristic butyric acid odor (rancid butter smell).
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org