All plastics

Acrylic (PMMA)

Commodity $$

Polymethyl methacrylate. The clearest economically-available rigid plastic — 92% light transmission, near-water clarity, rivaled only by special optical-grade PC and COC. Excellent UV resistance (the only commodity-tier clear plastic suitable for decades of outdoor service), hard scratch-resistant surface, easy solvent welding and edge polishing. Two production forms with meaningfully different properties — cast (higher MW, premium clarity and machining) and extruded (cheaper, easier thermoforming, lower clarity). The canonical "clear" plastic for signage, glazing, displays, museum cases, bathroom enclosures, lighting, and aquariums. The catch: brittle (4% elongation), only ~80°C continuous service, and attacked by most organic solvents.

Service °C
75–85°C continuous (167–185°F); short-term to 95°C
Tensile
60–75 MPa (8,700–10,900 psi); cast 70 MPa, extruded 65 MPa typical
Density
1.17–1.20 g/cm³ (0.043 lb/in³)
Cost
$$
$2.20/lb
Trade names: Plexiglas (Trinseo / Arkema, the original)Lucite (Lucite International, historical)Acrylite (Evonik)Optix (Plaskolite)Perspex (UK / Mitsubishi Chemical)Altuglas (Trinseo)Chemcast (Plaskolite cell-cast)

Polymethyl methacrylate. The clearest economically-available rigid plastic — 92% light transmission, near-water clarity, rivaled only by special optical-grade PC and COC. Excellent UV resistance (the only commodity-tier clear plastic suitable for decades of outdoor service), hard scratch-resistant surface, easy solvent welding and edge polishing. Two production forms with meaningfully different properties — cast (higher MW, premium clarity and machining) and extruded (cheaper, easier thermoforming, lower clarity). The canonical "clear" plastic for signage, glazing, displays, museum cases, bathroom enclosures, lighting, and aquariums. The catch: brittle (4% elongation), only ~80°C continuous service, and attacked by most organic solvents.

Properties

Mechanical
Mechanical properties for Acrylic (PMMA)
Tensile60–75 MPa (8,700–10,900 psi); cast 70 MPa, extruded 65 MPa typical
Yield55–70 MPa — acrylic yields very close to ultimate (brittle)
Elongation2–5% — defines acrylic as brittle; cast slightly lower elongation than extruded
Modulus2.9–3.3 GPa (420,000–480,000 psi)
Flexural100–115 MPa (14,500–16,700 psi)
Compressive75–130 MPa (11,000–19,000 psi)
HardnessRockwell M93–100 / Shore D 80 — among the hardest commercial plastics
Izod impact16–75 J/m notched (0.3–1.4 ft·lb/in) — brittle; impact-modified grades 70–250 J/m
Poisson's ratio0.4
Thermal
Thermal properties for Acrylic (PMMA)
Continuous max75–85°C continuous (167–185°F); short-term to 95°C
Short-term max90–100°C short-term
Min service-40°C — embrittles further at low temperatures but retains structural use
Conductivity0.17–0.21 W/m·K
CTE70–85 × 10⁻⁶/°C (39–47 × 10⁻⁶/°F) — significant for large glazed panels
Specific heat1260–1450 J/kg·K
Plastic-specific
Crystallinityamorphous
Tg100–115°C (212–239°F); cast acrylic ~110°C, extruded ~105°C
HDT85–105°C at 1.82 MPa / 95–115°C at 0.45 MPa (D648)
UL RTI~75°C (UL RTI)
Moisture (sat)0.3–0.6% at saturation
Water (24hr)0.2–0.4% (24hr immersion)
LOI17%
UL94HB
µ (friction)0.45

Variants (7)

Cast Acrylic (Cell Cast) cast
Trade: Plexiglas G, Acrylite GP, Chemcast, Perspex GS

Higher molecular weight, premium optical clarity, better mechanical properties, and superior machining behavior. Methyl methacrylate monomer polymerized in glass-faced cell molds. The choice for thick optical components (lenses, aquarium viewports, lighting), premium signage, and precision machined parts. 30–60% premium over extruded.

Extruded Acrylic extruded
Trade: Plexiglas MC, Acrylite FF, Optix

Lower molecular weight, cheaper, thinner-gauge-friendly, easier thermoforming, slightly worse mechanical and machining behavior than cast. The dominant commercial form for thin sheet (≤ 12 mm) used in signage, display, and general fabrication. Optical clarity is slightly lower than cast but visually equivalent in most uses.

Impact-Modified Acrylic impact-modified
Trade: Plexiglas DR, Acrylite Resist, Sumipex

Acrylic-elastomer alloy with significantly higher impact resistance at the cost of ~20% tensile and modulus. Approaches PETG-like toughness while retaining most of acrylic's clarity. ANSI Z97.1 safety-glazing grades available. The right choice for transit glazing, vending machine fronts, and impact-prone signage.

Abrasion-Resistant Coated Acrylic abrasion-resistant
Trade: Plexiglas AR, Plexiglas SAR (super abrasion-resistant), Acrylite AR

Hard-coated extruded acrylic for high-traffic glazing — bus shelters, ATM and vending fronts, retail display windows. The silica-based hard coat significantly improves scratch resistance without sacrificing optical clarity. Premium over standard extruded.

UV-Filtering Acrylic (Museum Glazing) UV-filtering-museum
Trade: Plexiglas OP-3, Acrylite Conservation Grade, Optium Museum Acrylic

UV-absorber-loaded acrylic blocking >98% of UV below 380 nm — used for museum and gallery framing to protect artwork from photodegradation. Maintains visual clarity. Premium over standard.

Optical-Grade Acrylic (Precision Cast) optical
Trade: Plexiglas G optical, Lumirror (PMMA optical film)

Precision-cast acrylic with low birefringence and tightly controlled refractive index (1.49). Used for diamond-turned optical lenses, light guides, fiber-optic claddings, and waveguides. Significantly higher cost than commodity cast acrylic.

Cast Acrylic Rod and Tube cast-rod-tube
Trade: Plexiglas G Rod, Acrylite Rod

Cast rod and tube stock for machining — displays, light guides, decorative architectural elements, prototyping. Better optical clarity and machining than extruded rod equivalents.

Processing

Machinability: excellent
Chip: Short brittle chips. Acrylic chips cleanly and predictably — one of the best-machining clear plastics. Cast acrylic chips slightly more crisply than extruded.
Gumming: Low to moderate. Acrylic Tg is 105°C — friction heat from dull tooling or aggressive feeds will gum the surface and craze the cut edge. Sharp tooling and adequate chip clearance are critical.
Finish: 16 Ra readily; 8 Ra with sharp finishing passes. Flame polishing and diamond polishing produce optically clear edges — the standard finishing method for acrylic glazing edges.
Tooling: Sharp carbide, neutral to slightly positive rake. Speed 500–1500 SFM (cast slightly slower than extruded). Feed 0.005–0.015 in/rev typical. Avoid dull tooling — dull tools generate heat that crazes the surface and causes stress-cracking weeks later. Mist coolant or air blast helps clear chips; flood coolant can craze acrylic surfaces.
Annealing at 75–80°C for 1 hr per 6 mm (1/4″) of section thickness is critical after heavy machining — relieves residual stress that causes crazing in solvent contact or under load over time. Skipped annealing is the #1 cause of acrylic field cracking in solvent-bonded assemblies. Bonding by solvent welding (methylene chloride, MEK, Weld-On) is excellent and is the standard joining method. Cyanoacrylates, structural acrylic adhesives, and epoxies also work well. Acrylic polishes optically — diamond turning produces optical surfaces for lens applications.
Process compatibility
injection molding excellent
extrusion excellent
cnc machining excellent
fdm poor
sla dlp good
sls not-applicable
mjf not-applicable
thermoforming excellent
blow molding poor
compression molding good

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Additives
uv stabilizer (0.5–1% UV absorber + HALS) — Acrylic is inherently UV-stable — among the most UV-resistant commercial plastics. UV-stabilized grades extend this further for premium outdoor and signage applications. Some grades go the other way — UV-filtering (Plexiglas OP-3) for museum preservation, blocking 98% of UV below 380 nm to protect art.
impact modifier (5–15% acrylic-modified rubber) — Impact-modified acrylic (Plexiglas DR, Acrylite Resist) approaches PETG-like toughness while retaining acrylic optical clarity. The right choice for high-traffic glazing and impact-prone signage. ANSI Z97.1 safety-glazing rated grades available.
mineral filler (silica-based hard-coat applied to surface (not bulk additive)) — Plexiglas AR / SAR, Acrylite AR are hard-coated extruded sheet for high-traffic glazing — bus shelters, vending fronts, ATM windows. Technically a surface coating rather than a bulk additive, but classified here for compositional purposes — the coating is a silica- or melamine-based hard layer applied to PMMA substrate, significantly improving scratch resistance.
colorant (0.05–3% pigment or dye) — Acrylic accepts virtually any colorant — fluorescent edge-glow grades (Plexiglas Fluorescent) are popular for signage; mirrored acrylic (vapor-deposited aluminum back) for displays.
flame retardant non halogen (15–25%) — FR-acrylic is uncommon — clarity is usually a key acrylic selection criterion, and FR systems destroy that. For clear flame-rated glazing, FR-PC is the standard choice.

Chemical resistance

acids fair Resistant to dilute non-oxidizing acids. Concentrated H₂SO₄, HNO₃ attack acrylic. Hot acids cause severe degradation.
bases good Resistant to most dilute and concentrated bases at room temperature. Strong alkalis at elevated temperature can hydrolyze the ester linkages over time.
aliphatic Solvents excellent Excellent in hydrocarbons, oils, fuels.
aromatic Solvents poor Aromatics (toluene, xylene, benzene) swell or dissolve acrylic. Used as solvent cements.
fuels Oils good Good in gasoline (some swelling), diesel, hydraulic oils at room temperature.
hot Water Steam fair OK in water at room temperature. Hot water above 60°C causes gradual hydrolysis of ester groups. Not for steam sterilization.
alcohols fair Resistant in unstressed state. Under load, isopropanol and other alcohols cause crazing — the canonical acrylic field failure. Common cleaner ingredient.
Acrylic's chemical resistance is moderate — far better than PS or PVC in atmospheric and aqueous service, much worse than polyolefins or PVDF in solvents. The defining acrylic chemistry issue is stress-craze sensitivity: stressed acrylic in contact with alcohols, ammonia cleaners (Windex), or many organic solvents develops surface crazes within hours to days. Unstressed acrylic in the same chemistry may be fine. Annealing reduces stress-crazing susceptibility significantly.
⚠ Stress-cracking agents
Alcohols under stress (isopropanol, ethanol — the classic field crazer)Ammonia and amine-based cleaners (Windex! — common cleaning failure)Ketones (acetone, MEK — used as acrylic solvents)Chlorinated solvents (methylene chloride — used for solvent welding)Aromatic hydrocarbons (toluene, benzene)Esters (ethyl acetate, plasticizers)Concentrated acids (oxidizing acids especially)Hot water and steam (long-term)

Regulatory

✓ FDA grade
✓ NSF 51
○ NSF 61
○ USP Class VI
✓ RoHS
✓ REACH
✓ EU 10/2011
HB UL94 best

Most clear acrylic grades meet FDA 21 CFR 177.1010 for food contact; NSF 51 grades available for food equipment glazing and shelving. UL94 HB only — acrylic burns readily and drips. FR-acrylic grades exist but significantly reduce optical clarity; for clear flame-rated glazing, polycarbonate FR is the better choice. No NSF 61 (potable water) — acrylic is not a primary water-system material. No USP Class VI medical grades — for clear medical, PETG or Tritan is the choice.

Notes & applications

Overview

Acrylic (PMMA) is the canonical clear plastic — 92% light transmission, near-water clarity, and the only commodity-tier plastic suitable for decades of outdoor service without yellowing. The polymer’s intrinsic UV stability (the methacrylate backbone is photochemically robust) is the property that makes acrylic the standard for signage, glazing, skylights, and any application where long-term clarity matters.

The two commercial forms have meaningfully different properties:

  • Cast acrylic — high molecular weight, polymerized from monomer in cell molds. Premium clarity, better mechanical properties, cleaner machining, higher cost. The choice for thick sections, optical components, precision machining, and aquarium viewports.
  • Extruded acrylic — lower MW, continuously extruded from PMMA pellets. Cheaper, easier thermoforming, slightly lower properties. Dominates commodity sheet for signage, display, and general fabrication.

The selection criteria for acrylic:

  • vs. Polycarbonate (PC) — acrylic is clearer (92% vs. PC’s 88%), harder, more scratch-resistant, far more UV-stable, easier to solvent-bond and polish. PC is 10× tougher in impact, has 50% higher service temperature, and is the safety-glazing standard. Pick acrylic for outdoor clarity, signage, displays, and museum cases. Pick PC for impact resistance, safety glazing, and elevated-temperature service.
  • vs. PETG — acrylic is clearer, harder, more scratch-resistant, more UV-stable. PETG is much tougher (110%+ elongation vs. 4%), easier to thermoform, BPA-free. Pick acrylic for static decorative use; pick PETG for parts that will be handled or impacted.
  • vs. Glass — acrylic is half the weight, 5–10× the impact strength, easier to fabricate, and shatters less catastrophically. Glass is harder, more scratch-resistant, and chemically tougher. For most modern signage and display, acrylic has displaced glass.

Acrylic’s killer features are near-water clarity, UV stability, and solvent bondability. The bonded transparency of acrylic-to-acrylic solvent joints — invisible to the eye — is the basis of the aquarium, display case, and architectural-glazing industries.

Machining notes

Acrylic is among the best-machining plastics — chips cleanly with sharp tooling, holds tight tolerances, polishes to optical finish. Cast acrylic machines slightly better than extruded (higher molecular weight, less prone to surface crazing).

Practical recipe:

  • Sharp carbide, neutral to slightly positive rake
  • Speed: 500–1500 SFM
  • Feed: 0.005–0.015 in/rev typical
  • Coolant: mist or air blast preferred — flood coolant can craze acrylic
  • Avoid dull tooling: dull tools generate heat that crazes the cut surface and produces stress that cracks the part weeks or months later

Annealing is critical for stressed parts. Heavy machining introduces residual surface stress. Annealing at 75–80°C for 1 hour per 6 mm (1/4″) of section thickness relieves this stress and dramatically reduces solvent-induced crazing in service. Skipped annealing is the #1 cause of acrylic field failures in solvent-bonded assemblies — the part looks fine after fabrication, then crazes and cracks weeks to months later when exposed to alcohols (cleaners) or environmental solvents.

Solvent welding is the canonical acrylic joining method. Methylene chloride or MEK applied between two acrylic surfaces dissolves a thin layer of each, then evaporates leaving a fused joint at near-parent strength. Done properly, the joint is optically invisible. Branded solvents (Weld-On 4, IPS Plastics Weld-On 16) are slightly thickened versions for easier application.

Edge polishing for optical-quality edges:

  • Flame polish — propane or hydrogen flame across the cut edge produces glass-like clarity, fast but heat introduces stress
  • Diamond polish — diamond-coated rotary cutter, optical-quality finish, used for premium and museum-quality work
  • Vapor polish — methylene chloride vapor exposure, very clean finish, used for laser-cut edges

Variant selection guidance

  • Cast acrylic (Plexiglas G, Acrylite GP) — premium clarity and mechanicals, the choice for thick optical, precision machining, and aquarium viewing panels. 30–60% premium over extruded.
  • Extruded acrylic (Plexiglas MC, Acrylite FF, Optix) — the workhorse commodity sheet for signage, display, retail fixtures, general fabrication. Lower cost, slightly lower properties.
  • Impact-modified (Plexiglas DR, Acrylite Resist) — for transit glazing, vending machine fronts, impact-prone signage. ANSI Z97.1 safety-glazing rated grades available.
  • Abrasion-resistant (Plexiglas AR, SAR) — high-traffic glazing. Hard-coated surface for scratch resistance.
  • UV-filtering (Plexiglas OP-3, Optium) — museum and gallery framing, artwork protection.
  • Optical-grade — precision-cast for diamond-turned lenses and light guides.
  • Cast rod and tube — machined display elements, light guides, prototyping.

Failure modes worth designing around

Brittle fracture is the dominant acrylic failure mode. At 2–5% elongation with no yield warning, acrylic shatters under impact or notched loading. Any sharp internal corner, drill hole edge, or stress concentration becomes a crack initiator. For impact loading or safety glazing, use impact-modified acrylic or step up to polycarbonate.

Solvent crazing under stress is the #1 acrylic field failure. The classic scenarios:

  • Acrylic glazing cleaned with ammonia-based glass cleaner (Windex) — surface crazes within months
  • Solvent-bonded display case in environment with airborne solvents (paint shop, dry cleaner) — crazes around joints
  • Acrylic mug filled with isopropanol — crazes immediately
  • Aluminum-on-acrylic vinyl letters with adhesive containing solvent — craze pattern visible after months

The mechanism: tensile stress (residual from machining or molding, or external load) + solvent contact = molecular-level crack initiation. Pure water cleaning, annealing of machined parts, and avoidance of alcohol-based cleaners are the field defenses.

Scratch sensitivity — though hard for a plastic, acrylic is much softer than glass. Repeated abrasive contact (cleaning with abrasive cloth, sand-laden traffic on transit glazing) abrades the surface. Abrasion-resistant coated grades address this for high-traffic applications.

UV exposure is rarely a failure mode — acrylic is among the most UV-stable commercial plastics. This is one of its defining strengths. Decades of outdoor exposure with minimal yellowing for unstabilized acrylic, 30+ years with UV-stabilized grades. The exception is solvent-welded joints under continuous UV — the joint zone can yellow and craze faster than parent material.

Heat distortion above 75°C — acrylic softens approaching Tg (~105°C). Sun-exposed enclosed spaces (cars, greenhouses) can reach temperatures that distort thin-section acrylic. For elevated-temperature service, specify polycarbonate.

Flammability — UL94 HB only. Acrylic burns readily with a clean flame and drips burning material. Not for fire-rated barriers.

Creep under sustained load — acrylic cold-flows over years under continuous tensile or compressive load. Bolted joints relax; gasket preload diminishes. Spring loading or design margin required.

Applications by industry

  • Signage — illuminated channel letters, monolithic faces, point-of- purchase displays. The single largest acrylic market by volume. Cast for premium signage, extruded for commodity.
  • Glazing and construction — sound barriers (highway sound walls), greenhouse panels, skylights, hurricane-resistant windows (with impact-modified or laminate construction), bus shelters, transit glazing.
  • Lighting — fluorescent and LED diffusers, light guides, signage illumination, lens-array light panels. Cast acrylic dominates light- guide applications.
  • Aquariums and marine — large public aquarium viewing panels (cast acrylic to >300 mm thick), home aquariums (cast acrylic alternative to glass), submarine viewports (specialty cast).
  • Retail and display — display fixtures, point-of-purchase signage, shelving, museum exhibition cases. The clarity and bondability are selling points.
  • Furniture — clear acrylic chairs (Ghost chair and similar), tables, modernist interior design pieces. Often impact-modified.
  • Photography and art — picture framing glazing (museum-grade UV- filtering acrylic protects artwork better than glass), display cases for art and historical artifacts.
  • Automotive — tail-light lenses (legacy; LED-direct designs reducing this), instrument cluster lenses, decorative interior trim.
  • Dental and medical — denture base material (specific medical PMMA grades), impression trays, lab equipment glazing. (Note: bone-cement PMMA used in orthopedic surgery is a different commercial form — self-curing two-component PMMA.)
  • Optics — precision cast lenses (camera, projector, fiber-optic collimators), light guides for instrumentation, waveguide cores.
  • Solar energy — transparent covers for solar collectors and concentrating solar systems. UV stability is the enabling property for decades of outdoor service.
  • Hobby and prototyping — clear sheet, rod, tube stock for hobby projects, model making, university lab prototyping.

Sources & standards

Standards: ASTM D788 (Acrylic plastic sheets and rods)ISO 7823 (Plastics — PMMA sheets)ANSI Z97.1 (safety glazing — impact-modified acrylic)FDA 21 CFR 177.1010 (acrylic food contact)NSF/ANSI 51 (food equipment materials)MIL-PRF-25690 (aircraft transparency PMMA)

Related commodity materials

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