Thermal properties of plastics
Plastics are, with a handful of exceptions, thermal insulators. Their thermal conductivity sits between 0.15 and 0.4 W/m·K — two orders of magnitude below aluminium — and only specially filled compounds break the 1 W/m·K barrier. Beyond conductivity, four numbers govern how a polymer behaves under heat: glass transition (Tg), melting point (Tm), heat deflection temperature (HDT) and continuous service temperature. This guide ranks common polymers on each of those metrics.
What to look for
- Thermal conductivity (W/m·K) — heat flow through the wall of the part
- Heat deflection temperature (HDT, °C) — short-term resistance under load
- Continuous service temperature (°C) — long-term ceiling in air
- Melting point / glass transition — processing and upper use limit
- Coefficient of thermal expansion (CTE) — dimensional stability across temperature
Top materials for thermal properties of plastics
- #1ABSAcrylonitrile Butadiene StyreneThermal Conductivity: 0.17 W/m·K
A tough engineering thermoplastic widely used in automotive, consumer products, electronics and 3D printing.
- #2PolycarbonatePolycarbonateThermal Conductivity: 0.20 W/m·K
A transparent, high-impact engineering plastic used in glazing, electronics and safety equipment.
Frequently asked
Most unfilled plastics fall between 0.15 and 0.4 W/m·K. Polyethylene sits near 0.4, polypropylene near 0.22, PVC near 0.19, and PEEK near 0.25. Thermally-conductive compounds with boron nitride or graphite fillers can exceed 5 W/m·K.
Filled thermally-conductive compounds (CoolPoly, TC-series PPS/PA6) lead by design. Among unfilled polymers, HDPE and PA are near the top; fluoropolymers and foams sit at the bottom.
HDT is the temperature at which a plastic deflects a set amount under load (usually 0.45 or 1.8 MPa, ISO 75). It is always well below the melting point and is the practical ceiling for load-bearing parts.
No true Tm — they soften gradually above their glass transition (Tg). ABS, PC, PMMA and PVC are amorphous; PE, PP, PA, POM, PEEK are semi-crystalline and have a sharp Tm.