Thermoplastic comparison
PET vs PETG (glycol-modified PET)
Every value below is a typical room-temperature figure with its source, test method and conditions — the same dataset that drives the calculators.
Which to choose
The same backbone with one deliberate change: the glycol in PETG suppresses crystallisation, which is exactly what makes it easy to print and reliably clear, where PET hazes and is far fussier to process. PET is the better barrier and is what drinks bottles are blown from; PETG is the one you print and thermoform.
| Property | PET | PETG (glycol-modified PET) | Difference |
|---|---|---|---|
| Density | 1.37 g/cm³ | 1.3 g/cm³ | PET — 5% higher |
| Young's modulus E | 2.9 GPa | 2.2 GPa | PET — 32% higher |
| Tensile strength | 60 MPa | 53 MPa | PET — 13% higher |
| Glass transition Tg | 76 °C | 81 °C | PETG (glycol-modified PET) — 5 °C higher |
Where these numbers come from
- Callister & Rethwisch, Materials Science and Engineering, 10th ed.
- MakeItFrom.com materials database — typical grade values
Typical room-temperature values for learning and preliminary design; grades vary widely and a supplier datasheet always overrides a textbook figure. Confirm against the datasheet before design work.