Polycarbonate Properties: Impact, Optical & Thermal Data
Polycarbonate delivers a rare combination: impact resistance 250 times greater than glass at 88% optical transmission, all within a continuous service window that reaches 240°F. Understanding the full property profile — mechanical, optical, thermal, electrical, and chemical — is essential before specifying PC for machine guards, glazing, or enclosures. This page provides datasheet-grade values with engineering context for each property family.
At a glance:
- Notched Izod impact 18 ft-lb/in; unnotched bars show no break
- Light transmission 88% clear grades; refractive index 1.586
- Continuous service temperature 240°F; Tg 302°F (150°C)
- Dielectric strength 400 V/mil; volume resistivity 10¹⁶ Ω·cm
- UL 94 V-2 standard; V-0 grades available; LOI 27%
- Poor UV stability without stabilizer — yellowing starts at 6–12 months unprotected
- Chemical resistance poor vs. aromatic solvents, acetone, strong alkalis
Mechanical Properties
Polycarbonate's mechanical profile is dominated by its extraordinary toughness. The carbonate linkage in the backbone allows chain rotation under stress, absorbing impact energy without crack propagation — the mechanism behind its unmatched Izod performance among unfilled transparent thermoplastics.
Impact Behavior Across Temperatures
Polycarbonate retains excellent impact resistance from -40°F down to cryogenic conditions, which is why it is used in aircraft instrument covers and cold-room windows. At 73°F the notched Izod sits at 18 ft-lb/in; at -40°F it drops to approximately 12 ft-lb/in — still dramatically higher than acrylic at room temperature.
Above the glass transition temperature of 302°F, the material becomes rubbery and loses all structural integrity. Between 240°F and 300°F, creep and deformation under sustained load become concerns even though the part hasn't failed catastrophically.
Scratch Resistance
Uncoated polycarbonate is significantly softer than glass and scratches readily — Barcol hardness is roughly 35. This is the material's primary limitation in abrasive environments. Hard-coat grades (Makrolon AR, Lexan Margard) apply a silicone-based abrasion-resistant coating that improves scratch resistance by 5–10× per ASTM D1044 Taber abrasion testing while retaining full impact performance.
Optical Properties
Light Transmission vs. Competing Transparents
Acrylic edges PC in raw transmission — 92% vs. 88% — and acrylic is often preferred where maximum clarity matters and impact resistance is secondary. The 4-percentage-point difference is perceptible in thick sections but negligible in panes under 0.25".
In applications where optics are critical (instrument lenses, camera covers), the higher refractive index of PC (1.586 vs. 1.49 for acrylic) can introduce slightly more reflective loss at each surface without anti-reflection coating. Lens designers account for this in optical stack calculations.
UV Behavior and Yellowing
Unprotected polycarbonate absorbs UV radiation at wavelengths below 380 nm, initiating photooxidation of the carbonate linkage. This produces a yellowing phenol compound visible as a yellow tint within 6–12 months of direct outdoor exposure. The impact properties are also degraded — surface crazing and embrittlement follow prolonged UV exposure.
UV-stabilized grades contain UV absorbers co-extruded into the surface or throughout the sheet. UV-coated Makrolon and Lexan SL grades are rated for 10-year outdoor performance with < ΔYI 3 change. For outdoor use without a UV-stable grade, apply UV-filtering window film or polycarbonate-compatible UV clearcoat.
Never specify uncoated general-purpose polycarbonate for permanent outdoor glazing. Use UV-stabilized grades (Makrolon UV, Lexan SL, Tuffak A) to prevent yellowing and surface embrittlement within the first year of service.
Thermal Properties
Coefficient of Thermal Expansion
The CTE of 3.8 × 10⁻⁵ in/in/°F (68 × 10⁻⁶ m/m/°C) is notably high compared to glass (0.5 × 10⁻⁵) or aluminum (1.3 × 10⁻⁵). For a 48" panel swinging 100°F, thermal movement is 0.18" — expansion slots and floating fasteners are mandatory in large glazing installations to prevent buckling or cracking at fastener points.
Thermoforming and Forming Temperature
PC softens uniformly above 340°F and is typically thermoformed at 340–375°F in a convection oven. Unlike semi-crystalline polymers, it has no sharp melting point, so the forming window is broad. Pre-drying at 250°F for 4–6 hours eliminates moisture that would otherwise create steam bubbles (silver streaks) in the formed part. Line bending with a strip heater is effective at the local scale — see the polycarbonate machining guide for parameters.
Electrical Properties
Electrical Applications
The combination of high dielectric strength (400 V/mil) and optical transparency makes polycarbonate useful for electrical inspection windows, control panel sight glasses, and instrument covers where both visibility and electrical isolation are required. The volume resistivity of 10¹⁶ Ω·cm means PC accumulates static charge readily — anti-static grades or surface treatments are used in semiconductor and cleanroom environments to prevent ESD.
Chemical Resistance
Polycarbonate's chemical resistance is a notable weakness relative to other engineering plastics:
| Chemical Class | Resistance |
|---|---|
| Aliphatic hydrocarbons (hexane, heptane) | Good |
| Dilute acids (HCl, H₂SO₄ <10%) | Good |
| Dilute alkalis | Good |
| Water, seawater | Good |
| Alcohols (methanol, ethanol) | Fair — some crazing with stress |
| Concentrated alkalis | Poor |
| Aromatic solvents (toluene, xylene) | Poor — dissolves/crazes |
| Ketones (acetone, MEK) | Poor — dissolves |
| Chlorinated solvents (MeCl₂) | Poor — used intentionally as cement |
| Gasoline, diesel | Poor — attack varies by formulation |
Do not use polycarbonate in contact with aromatic or chlorinated solvents, acetone, or strong alkalis. Even brief exposure to methylene chloride or toluene will craze and dissolve the surface. If chemical exposure is a concern, evaluate PETG, acrylic, or polypropylene depending on mechanical requirements.
For chemical resistance comparison across materials, see the polycarbonate comparisons page or review PETG material properties.
UV and Weathering Performance Summary
| Grade | UV Stabilizer | Rated Outdoor Life | Application |
|---|---|---|---|
| General purpose (Lexan 9034) | None | < 1 year (yellows) | Indoor only |
| Makrolon UV | Built-in UVA | 5 years | Standard outdoor |
| Lexan SL | Premium UVA + IR | 10 years | Architectural glazing |
| Tuffak A | UVA co-extruded | 10 years | Cost-effective outdoor |
| AR coated (Makrolon AR) | Yes | 5–10 years | Machine guard + outdoor |
For long-term outdoor glazing, specify a UV-stabilized grade and confirm the manufacturer's weathering guarantee (typically measured as ΔYI < 3 and no significant Izod reduction at the rated service life).
Order Polycarbonate to Your Specifications
Request polycarbonate sheet, rod, or tube with specific property requirements
Request a Quote →If the property profile above doesn't meet your application — particularly for higher temperature, better chemical resistance, or lower CTE — see the polycarbonate grades guide for glass-filled and specialty compounds, or evaluate acrylic sheet for indoor optical applications where impact resistance is a secondary consideration.
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Frequently asked questions — Polycarbonate FAQ