Acrylic vs Polycarbonate Windows: Which Is Better?

Acrylic and polycarbonate are the two clear plastics that replace glass, and they are sold side by side at every plastics supplier and home center. They look identical on the shelf. They are not. Polycarbonate, sold as Lexan, Makrolon, or Hyzod, is dramatically tougher and more flexible. Acrylic, sold as Plexiglas, ACRYLITE, OPTIX, or Perspex, is clearer, harder, cheaper, and stays clear in the sun without help. The wrong choice shows up as a window that goes milky in two seasons or one that cracks the first time a ball hits it.

The short version: polycarbonate when something is going to hit the window, acrylic for everything else. The long version is below, with the numbers.

The numbers

Sources for the figures are listed at the end. The impact multiples vary by test method and thickness, but the ranking does not.

Impact strength

This is polycarbonate's whole reason to exist. At about 250 times the impact resistance of plate glass and somewhere between ten and thirty times that of acrylic, polycarbonate is what riot shields, machine guards, and bullet-resistant glazing are made from. It does not shatter and it does not crack when you drill it. You can put a screw through a polycarbonate panel next to the edge and it will hold.

Acrylic is no slouch at around 17 times plate glass, and for a house, an RV, or a boat that is plenty. But acrylic fails by cracking, it cracks preferentially at drilled holes and sharp inside corners, and a big enough hit will break it. Where a window is going to be hit, by hail, by a baseball, by a boarding wave, or by a person trying to get in, polycarbonate is the answer and nothing else is close.

Clarity and light

Acrylic transmits about 92 percent of visible light, more than glass, with a colorless, neutral look at any thickness. Polycarbonate transmits 86 to 88 percent and carries a faint tint that grows with thickness. Side by side on a table, most people can pick the acrylic. In a single window on a house, most cannot. In a greenhouse, that four to six point difference is real light for the plants, which is one reason growers pay more for acrylic glazing.

Yellowing

This is where polycarbonate loses most of its arguments. Polycarbonate is not stable in ultraviolet light. Uncoated sheet yellows and goes milky, and the timescale in full sun is short. A boat owner on the YBW forum reported a polycarbonate wheelhouse window that had clouded after two seasons while the cast acrylic windows beside it were still pristine. Acrylic is UV-stable through the whole thickness of the sheet, with about 3 percent light loss over ten years outdoors, and ACRYLITE warrants it.

Modern polycarbonate solves this with a co-extruded UV-absorbing layer on one or both faces. UV-coated and "long-life" grades hold their clarity for ten to twenty years, and the greenhouse-panel industry depends on them. The catch is that the protection is a surface layer. Cut edges expose bare polycarbonate, a deep scratch goes through the coating, and you have to buy the coated grade and install the coated face out. Acrylic simply does not have the problem.

Scratching

Polycarbonate is soft. It scratches with a fingernail's worth of grit and it cannot be polished back, because the material smears rather than cuts. Acrylic is harder, scratches less, and, critically, can be wet-sanded and polished back to optical clarity with a kit costing under $40. Our scratch repair kit roundup covers exactly how. That difference is decisive for anything that gets cleaned regularly: a storm window, a boat hatch, a display case, an aquarium.

Hard-coated grades exist for both. Abrasion-resistant polycarbonate is what car headlights and aircraft windows use. Abrasion-resistant acrylic is the marine standard. Both cost considerably more than the plain sheet.

Heat and fire

Polycarbonate holds its shape to around 212 to 240°F, acrylic to around 180 to 190°F. Neither matters for a window, but it is why polycarbonate goes near engines and lights and acrylic does not.

Fire is the bigger deal. Under the International Building Code, light-transmitting plastics are classed by burn rate. Most polycarbonate qualifies as Class CC1, the better class, and is self-extinguishing. Acrylic burns steadily and is Class CC2. CC1 material is allowed in more building types and larger areas; CC2 comes with tighter limits, for example skylights capped at 25 percent of the floor area below against 33 percent for CC1. For a residential window or a greenhouse, both are generally permitted. For a commercial building, a large skylight, or anything near a property line, check the local code before choosing acrylic. Our acrylic vs glass guide has more on the classes.

Working with it

Polycarbonate is the easier material to fabricate on site. It cuts without chipping, drills without cracking, and cold-bends to a gentle curve without heat, which is why it goes on curved boat windshields and wraparound guards. Acrylic chips on the saw if you rush it, cracks at drilled holes without a proper bit and a pilot, and must be heated to bend. Thick acrylic, in one boat owner's words, has the bending ability of glass.

Acrylic wins on bonding and finishing. Solvent cement welds acrylic into a joint stronger than the sheet; polycarbonate bonds are weaker and fussier. Acrylic edges polish to glass-clear; polycarbonate edges stay matte.

The two also expand almost identically with temperature, about eight times as much as glass, so both need room in the frame and a flexible sealant. Sealant compatibility is the one place to be careful: some polycarbonate grades craze in contact with certain sealants and solvents, so use a product the sheet manufacturer lists as compatible.

Cost

Acrylic is cheaper. Supplier comparisons put polycarbonate at about 25 percent more for the same thickness; boat owners buying cast acrylic against polycarbonate report closer to 50 percent. Coated and abrasion-resistant grades of either widen the gap. At retail, a 4-by-8 sheet of twin-wall Lexan runs around $93, about $2.90 per square foot, which is cheap because twin-wall is mostly air; solid polycarbonate sheet is priced well above solid acrylic of the same gauge.

Where each one belongs

Choose polycarbonate:

• Hurricane and storm panels over windows
• Machine guards, security glazing, and anything that might be struck deliberately
• Hail-prone skylights and patio covers, in a UV-coated grade
• Curved windshields and guards that need to be cold-formed on site
• Anywhere the fire code requires CC1
• Twin-wall greenhouse glazing on a budget, again UV-coated, accepting the light penalty

Choose acrylic:

• Interior storm windows and inserts
• Flat boat windows, portlights, and hatch lenses, in cast or abrasion-resistant grade
• RV and camper windows, where the double-pane units are acrylic for a reason
• Aquarium, pool, and any thick viewing panel, where clarity at thickness decides it
• Display cases, picture framing, and anything that will be cleaned often and looked at closely
• Greenhouse glazing when light and longevity outweigh first cost
• Anything you want to polish, cement, or keep clear for twenty years without a coating

The tiebreaker. If you cannot decide, ask whether the window is more likely to be hit or to be scratched. Hit, polycarbonate. Scratched, acrylic. And if it will sit in full sun, only buy polycarbonate in a UV-coated grade, with the coated side out.

Sources

• Piedmont Plastics: Differences between acrylic and polycarbonate
• Acme Plastics: Polycarbonate vs. acrylic and Which is best, polycarbonate or acrylic panels?
• Interstate Plastics: Polycarbonate vs acrylic and Kastlite: Acrylic vs polycarbonate
• Erie Industrial Plastics: Polycarbonate, Lexan and Makrolon material data and The Lexan: Lexan multiwall polycarbonate sheets guide
• ACRYLITE: Acrylic sheet vs glass and ACRYLITE: Expansion and contraction of acrylic
• YBW Forum: Polycarbonate vs acrylic
• UpCodes: IBC Section 2610, light-transmitting plastic skylight glazing and Laird Plastics: Plastics for architectural glazing