PlasticsHow much heat can a plastic take? Continuous service, HDT, Vicat and melting point explained
The most frequent question when choosing a plastic is "how much temperature can it take?", and the answer has several layers: continuous service temperature is not the same as short-term temperature, deflection temperature under load (HDT), Vicat softening temperature or melting temperature. In this guide we explain what each one means and compare the temperatures of our twenty engineering plastics.
Five temperatures that don't mean the same thing
- Continuous service temperature: the range in which the part can work permanently without any appreciable loss of properties. It is the most useful figure when selecting a material.
- Maximum short-term temperature: the peak the material can withstand for a short time (minutes or hours), for example during a startup or a steam cleaning. It is not suitable for continuous service.
- Heat deflection temperature under load (HDT, ISO 75 / ASTM D648): the temperature at which a bar subjected to a bending stress of 1.80 MPa (method A) reaches a defined deflection while being heated at 120 °C per hour. It indicates how far the part stays rigid under load.
- Vicat softening temperature (ISO 306 / ASTM D1525): the temperature at which a 1 mm² flat-tipped needle penetrates 1 mm into the material under a load of 10 N (method A) or 50 N (method B). It marks the transition from solid to soft.
- Melting temperature (ISO 11357): the temperature at which the crystalline phase melts, measured by calorimetry (DSC). It applies to semicrystalline thermoplastics; amorphous ones such as polycarbonate or PETG have no defined melting point and thermosets do not melt.
For a part that works under load, HDT is usually the real limit, not the service temperature; for a part with no load, the continuous service temperature is the reference. Melting is never a design value: long before it melts, the material has already lost stiffness.
Temperatures of our engineering plastics
Reference values taken from our data sheets. A dash indicates that the data sheet does not report that value or that it does not apply (thermosets do not melt).
| Material | Continuous service | Short term | HDT | Vicat | Melting |
|---|---|---|---|---|---|
| Nylon M natural | −40 a 110 °C | 170 °C | — | — | 216 °C |
| Nylon SL black | −40 a 110 °C | 170 °C | — | — | 216 °C |
| Nylon HS blue | −40 a 120 °C | 180 °C | — | — | 216 °C |
| Nylon AL red | −40 a 110 °C | 160 °C | — | — | 214 °C |
| Nylon XL green | −40 a 110 °C | 160 °C | — | — | 213 °C |
| HD Polyethylene PE 300 | −73 a 82 °C | — | — | 125 °C | — |
| HMW Polyethylene PE 500 | −100 a 80 °C | — | — | 80 °C | 135 °C |
| UHMW Polyethylene PE 1000 | −200 a 80 °C | — | — | 80 °C | 135 °C |
| Ceramic UHMW Polyethylene | — | — | — | — | 132 – 138 °C |
| Acetal (POM) | −50 a 100 °C | — | 110 °C | — | 165 °C |
| Teflon (PTFE) | −260 a 260 °C | — | — | — | — |
| Polycarbonate (PC) | −50 a 100 °C | — | 130 °C | — | — |
| PEEK | −60 a 250 °C | 310 °C | 152 °C | — | 343 °C |
| PETG Copolyester | 60 °C | — | 72 °C | — | — |
| PET Polyester | −20 a 115 °C | 180 °C | 80 °C | — | 255 °C |
| Polypropylene (PP) | 0 a 100 °C | 150 °C | 90 °C | — | 162–167 °C |
| Bakelite | 135 °C | — | — | — | — |
| Celoron | 135 °C | — | — | — | — |
| G10 / FR4 | — | — | — | — | — |
| G11 | — | — | — | — | — |
What the table shows
- PEEK stands alone in its class: 250 °C continuous service, 310 °C short-term and a melting point of 343 °C. It is the choice when the process exceeds 150 °C.
- Thermosets do not melt: Bakelite and Celoron operate up to 135 °C, G10/FR4 is Class F (155 °C) and G11 is Class H (180 °C), with Martens thermal stability of 200 °C. They keep their shape under heat because they are cured, not melted.
- PET outperforms acetal in heat: 115 °C versus 100 °C continuous service, although its HDT (80 °C) is lower than acetal's (110 °C); under load, acetal stays stiffer.
- Polyethylenes perform well in the cold: UHMW PE 1000 reaches −200 °C and HMW PE 500 reaches −100 °C, but their upper limit is 80 to 82 °C.
- Teflon covers the widest range: from −260 to 260 °C, which is why it is used in cryogenics and in hot processes.
- Transparent plastics have low limits: PETG works up to 60 °C (HDT 72 °C) and polycarbonate up to 100 °C (HDT 130 °C).
How to choose by temperature?
- Up to 80 °C: polyethylene (PE 300, PE 500, PE 1000), polypropylene up to 100 °C, PETG up to 60 °C.
- From 80 to 120 °C: nylon (110 to 120 °C), acetal (100 °C), PET (115 °C), polycarbonate (100 °C).
- From 120 to 180 °C: Bakelite and Celoron (135 °C), G10/FR4 (155 °C), G11 (180 °C).
- Over 180 °C: PEEK (250 °C) and Teflon (260 °C).
- If there is also a mechanical load, check the HDT and allow a safety margin; if there are short peaks, check the short-term temperature.
In summary
- Continuous service, short-term, HDT, Vicat, and melting measure different things; continuous service (or HDT if there is a load) is what drives the design
- Polyethylenes and polypropylene cover up to 80 to 100 °C; nylon, acetal, PET, and polycarbonate up to 100 to 120 °C
- Thermosets withstand 135, 155 and 180 °C without melting
- PEEK (250 °C) and Teflon (260 °C) are the high-temperature options
Why buy your engineering plastics at NAT MAC?
We have more than 54 years of experience in the industry and ISO 9001 certified quality. We carry all ten families of engineering plastics, each with its own data sheet, and we help you choose the right material for your part, your load and your working environment.
- Material cut to the size you need
- Data sheets with verified properties for each grade
- Advice on choosing the right plastic for your load, temperature and environment
- Stock in bars, plates and bushings with delivery throughout Mexico
- Backed by ISO 9001 certified quality
Tell us what part you'll make, the conditions it operates in and the sizes you need, and we'll recommend the right material. Request your free quote.
Sources: NAT MAC Engineering Plastics data sheets and catalog; TecnoQuim (material data sheets); ZwickRoell, Heat deflection temperature (ISO 75 / ASTM D648); ZwickRoell, Vicat softening temperature (ISO 306 / ASTM D1525).
