Short answer: Check the masking film first: it's usually printed with the brand (Plexiglas, Acrylite, Optix for acrylic; Lexan, Makrolon, Tuffak for polycarbonate). Without a label, bend a scrap corner: acrylic is stiff and snaps (about 4 to 6% elongation), while polycarbonate flexes, whitens, and bends without breaking. Acrylic edges look clear or slightly green and polish to a glassy shine; polycarbonate edges often look faintly blue or gray. Acrylic is also harder and rings sharper when tapped. Don't laser-test unknown sheet: polycarbonate cuts badly and gives off harmful fumes.
Key facts
| Property | Acrylic (PMMA) | Polycarbonate (PC) |
|---|---|---|
| Common brands | Plexiglas, Acrylite, Optix, Lucite, Perspex | Lexan, Makrolon, Tuffak, Palsun |
| Specific gravity | 1.19 | 1.20 |
| Refractive index | 1.49 | 1.586 |
| Light transmission, 1/8 in. | 92% | 86% |
| Elongation at break | 4 to 6% | very high; yields and bends without breaking |
| Notched Izod impact | 0.3 to 0.4 ft-lb/in. | 12 to 16 ft-lb/in. |
| Rockwell hardness | M-93 to M-100 | M-70 |
| Flexural modulus | 450,000 to 490,000 psi | 345,000 psi |
| Heat deflection at 264 psi | 195 to 210 °F | 270 °F |
Acrylic values from ACRYLITE, Plexiglas G, and OPTIX data sheets; polycarbonate from the LEXAN 9034 data sheet.
Test 1: read the masking
New sheet almost always carries printed masking film or paper with the brand and often the grade and thickness. Plexiglas, Acrylite, Optix, Lucite, and Perspex are acrylic. Lexan, Makrolon, Tuffak, and Palsun are polycarbonate. If the masking is gone, keep going.
Test 2: the bend test (on a scrap or corner)
This is the most reliable at-home test. Clamp a thin offcut and bend it firmly. Acrylic barely bends and then snaps cleanly, because it stretches only about 4 to 6% before breaking. Polycarbonate bends a long way, turns white along the bend line, and usually stays bent without breaking, because it yields instead of fracturing. Wear safety glasses; acrylic snaps sharply.
Test 3: look at the edge
Look along a cut edge in daylight. Clear acrylic edges usually look water-clear or faintly green, and a polished acrylic edge is glassy. Clear polycarbonate edges often look faintly blue, gray, or yellowish, and stay a little dull even when sanded fine. It's a hint, not proof, since both can be tinted.
Test 4: scratch and tap
Acrylic is notably harder (Rockwell M-94 or so against M-70 for polycarbonate). Drag a fingernail or a coin edge across a hidden corner: polycarbonate marks more easily. Tap the sheet with a knuckle or fingernail: acrylic gives a sharper, higher "click"; polycarbonate sounds duller. Both are subtle, so compare against a known piece if you have one.
Test 5: how it cuts
On a saw, acrylic tends to chip at the edge if the blade is wrong; polycarbonate cuts cleanly, almost like hard wood, and doesn't chip. Drilling tells you too: acrylic throws powdery chips and can crack near an edge, polycarbonate throws long stringy curls. See how to drill acrylic.
Test 6: optical clues
Acrylic's refractive index is 1.49 against polycarbonate's 1.586. Thick polycarbonate looks a bit more "sparkly" and shows rainbow stress patterns more readily between polarizing filters, such as two pairs of polarized sunglasses crossed at 90°. Again, a supporting clue rather than a definitive test.
Tests to avoid
- Don't laser cut unknown sheet. Polycarbonate cuts poorly with a CO2 laser, scorches, and gives off fumes that shouldn't be breathed. Shops won't laser unidentified plastic for this reason.
- Skip the burn test unless you have proper ventilation and fire safety. Both plastics burn, and burn tests are easy to misread.
- Solvent tests are unreliable. Many solvents that attack acrylic, such as methylene chloride, attack polycarbonate too.
- Float tests don't work. At 1.19 and 1.20, both sink in water and their densities are too close to separate at home.
Why it matters which one you have
- Cutting: acrylic lasers beautifully with glossy edges; polycarbonate doesn't. See can you laser cut acrylic.
- Strength: polycarbonate is far tougher in impact; acrylic is stiffer, clearer, and more scratch resistant. See acrylic vs polycarbonate.
- Polishing: acrylic edges flame-polish and buff to clear; polycarbonate is much harder to polish.
- Heat: polycarbonate handles about 60 °F more before it softens under load.
Everything we cut is identified, branded sheet. Order acrylic parts in the instant quote.
Questions
Is plexiglass acrylic or polycarbonate?
Acrylic. "Plexiglas" is a brand of acrylic sheet, and "plexiglass" is used generically for clear acrylic. Lexan is the well-known polycarbonate brand. See acrylic vs plexiglass.
How do I tell acrylic from PETG?
PETG also bends without breaking, so the bend test separates it from acrylic but not from polycarbonate. PETG is softer and scratches very easily. See acrylic vs PETG.
Is polycarbonate heavier than acrylic?
Barely. Polycarbonate's specific gravity is 1.20 and acrylic's is 1.19, so you can't tell them apart by weight.