Quick3D Glass transition temperature (Tg)
The glass transition temperature is where a plastic turns from rigid to rubbery. Learn how Tg is measured and how it relates to heat resistance.
What it means in practice
Below its glass transition temperature (Tg), the disordered part of a plastic is locked in place. It is hard and stiff, like glass. Above Tg, the polymer chains can move. The material turns soft, rubbery and much less stiff.
Key takeaways
- Below Tg a plastic is hard and glassy; above it, the material turns soft and rubbery.
- Tg is not a melting point, but it often limits parts that must hold their shape.
- Amorphous plastics lose most stiffness at Tg; semi-crystalline ones hold on until melting.
- DSC and DMA give different numbers for the same material, so compare like with like.
Tg is not a melting point. Nothing turns liquid. But for many plastics it is the real limit for parts that must hold their shape.
Amorphous
Amorphous plastics (ABS, ASA, PC, PETG and most resins) lose most of their stiffness at Tg. Their useful temperature limit sits below it.
Semi-crystalline
Semi-crystalline plastics (PLA, nylon, PP, PEEK) also have crystals, which hold the part together above Tg until the melting temperature. How much they soften depends on how crystalline the part is.
- Elastomers such as TPU have a Tg well below room temperature. That is why they feel rubbery in normal use.
Tg matters for car interiors, parts near heat sources, dishwasher-washed items, and parts that must survive cold, where flexible materials can stiffen as they approach their Tg.
How it’s measured
- DSC (differential scanning calorimetry; ISO 11357-2, ASTM D3418): a small sample is heated slowly. Tg shows up as a step in the heat flow.
- DMA (dynamic mechanical analysis; for example ASTM D4065): a sample is gently flexed while heated. Tg is taken from the drop in stiffness or the peak of a damping curve called tan δ.
- Units: °C.
How to read and compare it
- Method changes the number. DMA tan δ values usually come out higher than DSC values for the same material. Compare like with like.
- Onset, midpoint or peak. Tg is a range, not a single point. Sheets may quote any of these.
- Heating rate. Faster heating tends to raise the reported Tg.
- Moisture. Water acts as a softener in nylons and lowers Tg.
- Resin cure. For photopolymers, Tg depends on how fully the part is post-cured.
- Not a service temperature. Use it with HDT, which reflects behaviour under load.
Range in our catalog
- All materials: -107–247 °C (median 81 °C, 212 materials)
- Filaments: -44–247 °C (median 96.35 °C, 146 materials)
- Resins: -107–175 °C (median 60 °C, 47 materials)
- High-performance materials: 83–247 °C (median 186 °C, 33 materials)
- Flexible materials: -107–37 °C (median -32.75 °C, 18 materials)
Good to know
Negative values are normal for elastomers.
- PLA 2850–63
- PA6 767–76
- PETG 1369.7–85
- ABS 12101–126.3
- ASA 698–112
- PC 11113–161
- PEEK 4143–143
- PEI 12177.3–217
Bar = lowest to highest, dot = median. 93 materials, live from our database.
Highest and lowest in our catalog
Highest Tg
| Material | Polymer | Glass transition temperature |
|---|---|---|
| 3DXTECH ThermaX TPI | TPI | 247 °C |
| 3DXTECH ThermaX PPSU | PPSU | 230 °C |
| Stratasys PPSF | PPSU | 230 °C |
| Ultrafuse PPSU | PPSU | 222 °C |
| Formfutura PPSU | PPSU | 220 °C |
Lowest Tg
| Material | Polymer | Glass transition temperature |
|---|---|---|
| Formlabs Silicone 40A Resin | Silicone | -107 °C |
| Formlabs Flexible 80A Resin V2 | Photopolymer | -49 °C |
| Ultrasint TPU 01 | TPU | -48 °C |
| Ultrasint TPU 88A | TPU | -48 °C |
| Ultrasint TPU 88A Black | TPU | -48 °C |
Related properties
- Heat deflection temperature — heat resistance under load.
- Vicat softening temperature — where the surface softens.
- Melting temperature — the second transition for semi-crystalline plastics.
- Impact strength — affected by how close you are to Tg.
See materials with a Tg of 100 °C or more 92 materials