Material selection
Polycarbonate vs Acrylic (PMMA)
Both are the default clear thermoplastics on this site, and both are stocked and processed here. The choice almost always comes down to one property: whether the part needs to survive an impact, or needs to hold its scratch-free finish and clarity outdoors for years. The numbers below are the same published values used on each material's own page, set side by side.
| Polycarbonate | Acrylic (PMMA) | |
|---|---|---|
| Density | 1.20 g/cm³ | 1.18 g/cm³ |
| Tensile strength | 60–70 MPa | 70–75 MPa |
| Flexural modulus | 2.3 GPa | 3.1 GPa |
| Heat deflection (1.8 MPa) | 130 °C | 95 °C |
| Mold shrinkage | 0.5–0.7 % | 0.3–0.6 % |
| Light transmission | 88 % (clear) | 92 % |
| Relative cost | Medium | Low |
Published values for unfilled grades at 23 °C unless stated, taken from each material's own datasheet page. Confirm against the supplier datasheet for the grade you specify.
What Polycarbonate is
Polycarbonate is the material you specify when a clear part has to survive being dropped, hit, or loaded near its limit without shattering. Notched Izod impact is roughly ten times that of acrylic, and it fails by yielding rather than cracking. It is rated for continuous use around 115-125 °C, but it is chemically sensitive: many solvents, alkalis, and some cleaning agents cause stress cracking, and combined tensile stress with solvent exposure is its classic failure mode.
What Acrylic (PMMA) is
Acrylic is the clearest common plastic, transmitting 92 percent of visible light, more than glass or polycarbonate, and it holds that clarity outdoors for decades where polycarbonate yellows. Its surface is hard enough to resist the fine scratching that dulls PC lenses in service. The trade-off is brittleness: notched impact strength is around a twentieth of polycarbonate's, and it fails by cracking with no yield warning.
Polycarbonate against Acrylic (PMMA)
| Polycarbonate | Acrylic (PMMA) | |
|---|---|---|
| Impact toughness | Roughly ten times the notched impact strength of acrylic; fails by yielding rather than cracking, the material to choose when a part will be struck or dropped | Around a twentieth of polycarbonate's notched impact strength; fails by cracking with no yield warning, a poor choice wherever a sudden load is expected |
| Optical clarity and scratch resistance | 88 percent light transmission and scratches relatively easily; an unprotected lens dulls with handling and usually needs a hard coat | 92 percent transmission, higher than PC, and a harder surface that resists the fine scratching that dulls PC lenses in service |
| Outdoor and UV stability | Yellows and loses clarity after years outdoors unless a UV-stabilised grade is specified | Holds its clarity and surface finish outdoors for decades without needing a separate UV-stabilised grade |
| Heat resistance | 130 °C heat deflection unfilled, rated for continuous use around 115-125 °C | 95 °C heat deflection, lower than polycarbonate |
| Stiffness | 2.3 GPa flexural modulus | 3.1 GPa flexural modulus, stiffer than polycarbonate |
| Processing caution | Must be dried below 0.02 percent moisture (typically 4 hours at 120 °C) or it hydrolyses in the barrel and loses most of its impact strength permanently, a defect that is not visible until the part is in service | Dried 2-4 hours at 80 °C; wet material shows up immediately as bubbles in the clear part, an easy defect to catch before it ships |
| Relative cost | Medium | Low, the cheaper of the two |
Which one, for which part
- Machine guards, safety lenses, and covers that must survive being struck or dropped favour polycarbonate: roughly ten times acrylic's notched impact strength, and it yields rather than cracks.
- Display windows, signage, and light guides where outdoor clarity has to last for years favour acrylic, which does not yellow the way unstabilised polycarbonate does.
- A clear part that also has to resist fine scratching from routine handling favours acrylic: a harder surface and higher flexural modulus than polycarbonate.
- Structural clear housings that need a flame-retardant or medical-grade documented material favour polycarbonate, which has widely used FR and medical grades; acrylic has no equivalent at that scale.
- Cost-sensitive optical parts with benign service, point-of-sale displays and instrument faces favour acrylic for its lower relative cost and cleaner machined finish.
Our status
Trumould runs both polycarbonate and acrylic in-house through injection molding and CNC machining; polycarbonate is also available through 3D printing for functional prototypes, acrylic is not offered through 3D printing here. Send the part, its service environment, and target volume, and the quote states which of the two is recommended and why, not just a price for whichever one you asked about first.
Specifying this part?
Send your CAD and target volumes. We come back with a price, a lead time, and any material or design notes that would reduce either.