PMMA vs Polycarbonate
PMMA and Polycarbonate are commonly confused, and 2 measured properties separate them — density most clearly.
PMMA vs Polycarbonate
PMMA
Clearer than glass and it shatters into blunt pieces — the aquarium wall, the aircraft canopy, the signage and the museum case.
Polycarbonate
Transparent and almost unbreakable — the safety glazing, the riot shield, the headlamp lens and the spectacle lens.
| Property | PMMA | Polycarbonate |
|---|---|---|
| Density | 1.17–1.2 g/cm³ | 1.2–1.22 g/cm³ higher |
| Refractive index Only one of the two has a figure we can stand behind, so there is nothing to compare. | 1.49 | Not known |
| Tensile strength | 65–75 MPa higher | 55–75 MPa |
| Young's modulus Only one of the two has a figure we can stand behind, so there is nothing to compare. | 2.4–3.3 GPa | Not known |
Choosing between them
PMMA is recorded as a substitute for Polycarbonate — cheaper, easier to work.
What it gives up: Cracks where polycarbonate deforms. PMMA absorbs a small fraction of the impact energy, so anywhere the requirement is not shattering it is the wrong one of the two.
In this application, on the evidence cited above.
Why these get confused
sold under trade names, both clear, and routinely substituted for each other by people who need the one that does not shatter. Perspex cracks; polycarbonate does not
The confusion is a real and documented one, not a resemblance we have invented.