Material selection
Both are clear, both machine well, and the price difference is large. The choice comes down to what could hit the part, what will clean it, and whether it will be outdoors.
Almost every clear part we quote could be made in either material, and the customer usually has a preference before the requirement is stated. That is the wrong order. Acrylic and polycarbonate differ on five properties that actually matter in service, and once you state the four facts below, the material chooses itself.
Answer those and the rest of this page is confirmation rather than decision-making.
| Property | Acrylic (cast PMMA) | Polycarbonate (PC) | What it means |
|---|---|---|---|
| Impact strength | Low — cracks rather than deforms | Very high — about 200× tougher than glass, 10–20× acrylic | The single biggest differentiator. Anything that could be struck is PC. |
| Optical clarity | 92% transmission, water-white | 88–90%, slightly warmer | Acrylic reads cleaner in a display. The difference is visible side by side. |
| UV stability | Excellent — clarity holds 10+ years | Poor — yellows in 3–5 years outdoors | Outdoor signage is acrylic. Uncoated PC outdoors is a maintenance item. |
| Surface hardness | Harder, polishes to glass clarity | Softer, scratches easily, hard to polish | Any part that is wiped daily or looked at closely favours acrylic. |
| Chemical resistance | Attacked by ketones, esters, aromatics, chlorinated solvents | Attacked by alkalis, ammonia, some solvents; better on hydrocarbons | The cleaning product decides more failures than the load case does. |
| Service temperature | Up to ~80 °C continuous | Up to ~115 °C continuous | Near a heat source, PC. Indoor ambient, either. |
| Thermal expansion | 0.07 mm/m·°C | 0.065–0.07 mm/m·°C | Effectively the same; both need slotted fixings. |
| Machining | Cuts, routes, drills, polishes predictably | Gums, needs sharp tooling and lower feed | Acrylic gives a better finished edge for the same effort. |
| Bonding | Solvent bonds to a near-invisible joint | Needs adhesive, joint shows | Display and vitrine work is acrylic for this reason alone. |
| Relative cost | 1.0 (baseline) | 1.6–2.2× acrylic for the same thickness | At equal thickness PC costs more; at equal impact resistance, far more. |
Most parts are not close. A retail display is acrylic, a machine guard over moving tooling is polycarbonate, an outdoor sign is acrylic, a barrier a person could fall against is polycarbonate. The genuinely ambiguous cases are these:
A standard cobot cell sees no impact, so acrylic at 5 mm is correct and looks better. A cell with a high-speed gantry or a part that can be ejected needs polycarbonate on the lower 800 mm and can keep acrylic above eye level. Splitting the guard by height is the usual answer, and it is cheaper than making the whole thing in PC.
Sneeze guards and queue barriers are reached for, leaned on and occasionally struck. Acrylic at 6–8 mm is standard and acceptable where the barrier is not designed to stop a person. Where it is a fall-protection barrier or a crowd barrier, the design load is a person, and the material is polycarbonate or laminated glass, not acrylic.
Occasional isopropyl wipes are tolerated by cast acrylic. Daily wiping concentrates stress at holes and bends and will craze the part within a year or two. Either move to a hard-coated acrylic, which resists it much better, or move to polycarbonate and accept the scratching.
Comparing price per square metre at the same thickness makes polycarbonate look like a 2× premium. That is the wrong comparison when the part is chosen for impact: to match the impact performance of 6 mm polycarbonate you would need something like 15–20 mm of acrylic, which is heavier, more expensive and no longer the cheaper option.
| Duty | Acrylic solution | Polycarbonate solution | Cheaper in practice |
|---|---|---|---|
| Display, indoor, no impact | 5 mm cast acrylic | Not used | Acrylic by a wide margin |
| Machine guard, no impact hazard | 5 mm cast acrylic | 5 mm PC, over-specified | Acrylic |
| Machine guard, chip or part ejection | Not suitable | 6 mm PC | PC — acrylic would fail |
| Public barrier, lean-on only | 8 mm acrylic | 6 mm PC | Acrylic |
| Public barrier, person impact | Not suitable | 10 mm PC or laminated glass | PC |
| Outdoor sign, 10-year life | 5 mm UV cast acrylic | PC with UV coat, replaced at 5 years | Acrylic over the life |
The failure we are asked to replace most often is acrylic used where polycarbonate was needed — a guard panel that cracked from an impact, or a barrier that shattered. The reverse mistake (PC where acrylic would do) costs money rather than safety, and is far more common in the other direction: customers over-specifying PC and then complaining that it scratches.
A drawing that says only "clear plastic, 5 mm" will be quoted in whatever the fabricator has on the shelf. State the material, the grade and the reason:
MATERIAL: cast PMMA, clear, 5 mm, ±10% thickness — use cast, not extruded, for anything machined or bonded.GRADE: UV-stabilised for anything outdoors, ESD (10^6–10^9 Ω/sq) near electronics, UL 94 V-0 where a fire assessment requires it.EDGE: diamond polished, both faces filmed — polish is a separate operation and a separate line on the quote.FIXING: Ø8 holes for M6, slotted ±3 mm on the long axis, nylon washers, no thread in sheet.CLEANING: [product name] — this single line prevents most crazing failures.SERVICE TEMP: −10 to +45 °C — this decides the fixing detail as much as the material.If the application genuinely needs polycarbonate, the drawing should say so and should also say whether it needs a hard coat, because uncoated PC in a handled application looks tired within a year.
Polystyrene (PS) is cheaper and clearer than acrylic but brittle and easily crazed — it belongs in disposable packaging, not in a part with a service life. PETG sits between acrylic and polycarbonate on impact, bonds and bends well, and is the usual choice for a part that must not shatter but does not need PC-level toughness. Glass is heavier, breaks, and cannot be machined on the same equipment, but it is the only one of the group that will not scratch at all.
For a like-for-like table across all six materials, see the material comparison chart; for the process side of the same decision, the thickness and span guide covers how the choice changes the panel dimensions.
Only roughly. PC is softer and smears under a polishing pad, so the edge never reaches the water-clear finish a diamond-polished acrylic edge does. For a display part judged at close range, PC cannot substitute for acrylic on appearance.
Acrylic, unless impact is a real risk. Acrylic holds its clarity for a decade or more in UV; polycarbonate yellows in three to five years unless it carries a UV-resistant coating, and even then the coating is a wear item.
It expands slightly more and is more sensitive to over-tightening, so the same rules apply with a little more clearance: oversized holes, washers, and no thread cut into the sheet. PC also stress-crazes at fixing points if it is clamped hard.
Acrylic is not intended as a direct food-contact cutting surface because it scratches and harbours bacteria. As a display barrier or a sneeze guard it is standard. For direct contact, PE or PP is the correct material.
UV degradation of the polymer itself. It is not surface dirt and cannot be cleaned off. Replacement with acrylic (if impact allows) or with a UV-coated PC grade is the only fix.
Tell us what the part has to survive — impact, cleaning chemical, UV, temperature — and we will specify the material and the fixing detail together.