Materials / Compare
Glass vs. Plastic PETG
Compare Glass vs. Plastic PETG strength, stiffness, weight and thermal properties.
| Try it on a partA sample part to run stress or thermal on, free in your browser | Open in LessCAD | Open in LessCAD |
|---|---|---|
| Mechanical | ||
| Yield strength | not given (tensile used) | 46.2MPasourcetypical |
| Ultimate tensile strength | 41MPasourcetypical mean surface tensile stress at fracture (MOR), 60 s load, weathered, 50% breakage probability | 46.2MPasourcetypical, peak stress (= stress at yield) |
| Flexural strength | 41MPasourcemean MOR (same value as tensile) | 78.9MPasourcetypical |
| Elongation at break | not sourced | 7.6%sourcetypical |
| Young's modulus (stiffness) | 72GPasourcetypical37.1x stiffer | 1.94GPasourcetypical |
| Density | 2,500kg/m³sourcetypical | 1,270kg/m³sourcetypical1.97x lighter |
| Strength to weight | 16.4kN·m/kg | 36.4kN·m/kg2.22x higher |
| Stiffness to weight | 28.8MN·m/kg18.9x higher | 1.53MN·m/kg |
| Poisson's ratio | 0.22sourcetypical | not sourced |
| Shear modulus | 29.5GPa | not sourced |
| Bulk modulus | 42.9GPa | not sourced |
| Speed of sound | 5,367m/s | 1,236m/s |
| Thermal | ||
| Thermal conductivity | 0.937W/m·Ksourcetypical at 75 F | 0.21W/m·Ksourcebase material: Eastman Eastar Copolyester 6763 (PETG), typical |
| Thermal expansion | 8.3µm/m·Ksourcetypical, 75-575 F | 51µm/m·Ksourcebase material: Eastman Eastar Copolyester 6763 (PETG), typical |
| 100 mm part over a 50 °C swing | 41.5µm growth6.14x less | 255µm growth |
| Specific heat | 880J/kg·Ksourcetypical at 75 F | 1,300J/kg·Ksourcebase material: Eastman Eastar Copolyester 6763 (PETG), DSC at 60 °C (lowest temperature listed) |
| Heats up and cools (diffusivity) | 0.426mm²/s3.35x faster | 0.127mm²/s |
| Thermal shock resistance | 50.1W/m | not sourced |
| Glass transition | not sourced | 77.4°Csourcetypical |
| Max service temperature | 511°Csourcestrain point (ASTM C336) - stress-relaxation onset, not a rated service limit | 76.2°CsourceHDT 0.455 MPa (printed specimens) |
| Values for | Annealed soda-lime-silica float glass, Pilkington North America Technical Bulletin ATS-129 (04/2025) | Ultimaker PETG, 3D-printed specimens, XY (flat); Ultimaker S5 Pro, engineering intent profile, 0.15 mm layer height, AA 0.4 print core, 100% infill, Cura 4.9, printed one-at-a-time, conditioned >=24 h at room temperature. TDS v1.00, April 29, 2022. |
Every value links to the document that states it. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.
Plastic PETG is 3D printed: its properties depend on build direction and print settings; these are typical values.
Questions
Is Glass stronger than Plastic PETG?
Plastic PETG is stronger: its yield strength is 46.2 MPa against tensile strength 41 MPa for Glass (13%).
Which is lighter, Glass or Plastic PETG?
Plastic PETG is lighter: 1,270 kg/m³ against 2,500 kg/m³ for Glass.
Which is stiffer, Glass or Plastic PETG?
Glass is stiffer: Young's modulus 72 GPa against 1.94 GPa for Plastic PETG, so the same part in Glass deflects less under the same load.
Which is lighter for the same job, Glass or Plastic PETG?
For the same stiffness or strength: Glass is lighter for a stiff rod or tie (tension), stiff beam (bending), stiff panel or plate; Plastic PETG is lighter for a strong rod or tie, strong beam, strong panel or plate.
| Part that must be | Glass | Plastic PETG |
|---|---|---|
| Stiff rod or tie (tension) | lighter | 18.9x heavier |
| Stiff beam (bending) | lighter | 3.1x heavier |
| Stiff panel or plate | lighter | 1.69x heavier |
| Strong rod or tie | 2.22x heavier | lighter |
| Strong beam | 2.13x heavier | lighter |
| Strong panel or plate | 2.09x heavier | lighter |
For the same stiffness or strength, mass scales with density over stiffness (or strength) raised to a power set by how the part is loaded: 1 for a rod in tension, 1/2 for a beam in bending, 1/3 for a panel (the standard material-selection indices).
Which conducts heat better, Glass or Plastic PETG?
Glass conducts heat better: 0.937 W/m·K against 0.21 W/m·K for Plastic PETG.
Which expands less with temperature?
Glass expands less: 8.3 µm/m·K against 51 µm/m·K for Plastic PETG.