Polycarbonate vs Acrylic: Properties, Machinability & Cost Compared

Polycarbonate (PC) and acrylic (PMMA) rank as the two most widely specified transparent engineering plastics — yet they serve fundamentally different engineering roles. Polycarbonate delivers roughly 40 times the impact resistance of acrylic, while acrylic transmits more light (92% vs. 88%) and costs 30–40% less per kilogram. Choosing the wrong one leads to cracked safety glazing, yellowed outdoor enclosures, or overspent material budgets.

This guide compares polycarbonate and acrylic across mechanical properties, optical performance, thermal limits, chemical resistance, CNC machinability, outdoor durability, and total project cost. Each data point references ASTM test methods or manufacturer technical data sheets for independent verification. Boundary note: this article covers material selection and property comparison. For CNC process parameters specific to acrylic parts, see KUSLA Prototype’s acrylic CNC machining service. For ABS as an alternative to polycarbonate, see the ABS vs. polycarbonate comparison.

1. Polycarbonate vs. Acrylic at a Glance

The table below summarizes the core engineering properties of unfilled polycarbonate and cast acrylic sheet. All values reference ASTM standard test methods; cells highlighted in green indicate the superior material for that property.

Data compiled from iPolymer technical data sheets (ASTM-referenced), Protolabs engineering resources, and Xometry material guides. ✅ All mechanical values verified against 2+ independent sources.

The summary reveals a clear pattern: polycarbonate dominates in impact resistance, thermal endurance, and moisture resistance, while acrylic leads in optical clarity, surface hardness, UV stability, and cost. Neither material is universally superior — the right choice depends on the specific load case, operating environment, and budget constraints of each project.

2. Impact Resistance: Why the 40× Gap Changes Part Design

The most dramatic difference between polycarbonate and acrylic lies in impact behavior. Unfilled polycarbonate achieves a notched Izod impact strength of 694 J/m (13 ft-lb/in per ASTM D256), compared to just 16 J/m (0.3 ft-lb/in) for acrylic.✅ That 43:1 ratio is not a marginal engineering difference — it determines whether a part cracks on first impact or survives repeated abuse.

How Each Material Fails Under Impact

Acrylic is a brittle thermoplastic. At 2% elongation at break, it absorbs almost no energy before fracturing. When an acrylic panel receives a sharp impact, it shatters into angular fragments — similar to glass but lighter. This brittleness makes acrylic unsuitable for any application where human contact with broken material is possible, such as machine guards, face shields, or vandal-prone glazing.

Polycarbonate behaves as a ductile material, stretching to 60% elongation before failure.✅ Under impact, it deforms plastically — denting or bowing rather than fracturing. Even at extreme loads, polycarbonate panels tend to stay in one piece, which is why the material dominates in bullet-resistant glazing, riot shields, and safety goggles (ANSI Z87.1 rated). The trade-off is that surface denting and stress whitening can occur at impact sites, affecting optical clarity locally.

Design Implications: Wall Thickness and Weight

The impact gap directly affects wall thickness decisions. A polycarbonate machine guard at 3 mm thickness often provides equivalent protection to a 6 mm acrylic panel — cutting part weight nearly in half while improving safety. For enclosures and housings where drop-test survival matters (such as portable instrument cases), polycarbonate allows thinner walls and more compact designs.

3. Optical Clarity, Haze, and UV Stability Over Time

For applications where visual clarity is the primary specification — display cases, light guides, optical lenses, LED diffusers — the 4-percentage-point gap in light transmission between acrylic (92%) and polycarbonate (88%) is significant.✅ To put this in context, standard float glass transmits approximately 90% of visible light, meaning acrylic actually outperforms glass optically.

Refractive Index and Optical Distortion

Acrylic’s refractive index of 1.49 sits closer to glass (1.52) than polycarbonate’s 1.58.✅ Higher refractive indices increase the angular deviation of transmitted light, which means polycarbonate panels — particularly at thicknesses above 6 mm — can produce noticeable optical distortion when viewed at oblique angles. For museum display cases, retail fixtures, and precision optical components, acrylic delivers truer image transmission.

UV Degradation: The Yellowing Timeline

This is where acrylic holds a decisive long-term advantage. PMMA is inherently UV-stable: the molecular structure absorbs minimal ultraviolet radiation, so uncoated acrylic maintains optical clarity for 10–15 years of direct outdoor exposure with negligible yellowing.✅

Standard polycarbonate, by contrast, degrades under UV exposure. Uncoated PC sheets begin showing measurable yellowing (Δb* > 2 on the CIE Lab scale) within 2–3 years of outdoor use. The degradation mechanism involves photo-Fries rearrangement and photo-oxidation of the bisphenol A backbone, which produces yellow chromophores on the surface layer.

UV-stabilized polycarbonate grades (coated or co-extruded with UV-absorbing layers) extend outdoor life to 10+ years, but they add 15–25% to sheet cost and introduce a coating that can delaminate if the sheet is machined after coating.

4. Thermal Performance and Dimensional Stability

Polycarbonate tolerates significantly higher operating temperatures than acrylic. With a heat deflection temperature (HDT) of 132°C at 264 psi (ASTM D648) versus 65–100°C for acrylic, polycarbonate maintains structural rigidity in environments where acrylic begins to soften and deform.✅

Glass Transition and Continuous Service Limits

Polycarbonate’s glass transition temperature (Tg) of 145°C (ASTM D3418) provides a wide safety margin above its recommended continuous service limit of 121°C.✅ Acrylic’s continuous service limit of 65–93°C (varying by grade) means it is unsuitable for applications near heat sources — LED housings that generate significant waste heat, under-hood automotive components, or sterilizable medical device enclosures.

Thermal Expansion Considerations

Both materials share a similar coefficient of linear thermal expansion (CTE): approximately 3.9 × 10⁻⁵ in./in./°F for polycarbonate and 5–9 × 10⁻⁵ in./in./°F for acrylic (ASTM D696).✅ However, acrylic’s higher CTE range means larger panels (over 600 mm in any dimension) require expansion gaps in frame designs to prevent buckling. Polycarbonate’s tighter CTE range simplifies mounting and frame engineering for large-format panels.

Polycarbonate’s lower thermal conductivity (1.3 vs. 3.9 BTU·in/ft²·hr·°F) also makes it a marginally better thermal insulator — relevant for skylights and architectural glazing where thermal bridging contributes to energy loss.✅

5. Chemical and Solvent Resistance Matrix

Neither polycarbonate nor acrylic qualifies as chemically resistant in the way that HDPE or PTFE does. Both materials are vulnerable to specific chemical families, but the attack vectors differ — and getting this wrong in design can cause sudden stress-crack failure months after installation.

Acrylic, while resistant to a broader range of common cleaners, has its own vulnerability: it crazes readily when exposed to ketones or aromatic hydrocarbons. The crazing pattern — a network of fine surface micro-cracks — is irreversible and progressively degrades optical clarity. For laboratory or industrial environments with solvent exposure risk, neither material may be sufficient; consider PETG or specialty grades.

6. CNC Machinability: Cutting Parameters and Shop-Floor Guidance

Both polycarbonate and acrylic machine well on standard CNC milling and turning centers, but they demand different strategies. The primary concern with acrylic is chipping and cracking; with polycarbonate, it is heat buildup and gumming. KUSLA Prototype machines both materials daily — the following parameters reflect production-validated settings.

Acrylic Machining Tips

Acrylic’s brittleness means aggressive climb milling or dull tools cause edge chipping. Single-flute “O-flute” end mills with polished flutes are the standard choice — the open flute geometry evacuates chips efficiently without re-cutting, and the polished surface reduces friction heat. Back-support the workpiece on flat vacuum fixtures or double-sided tape to prevent vibration-induced cracking on thin sheets (<3 mm). Acrylic machines to near-optical surface finish directly off the tool when parameters are dialed in — many display and lens applications skip post-polishing entirely.

Polycarbonate Machining Tips

Polycarbonate’s low melting point relative to its cutting temperature window makes heat management the primary challenge. Dull tools, insufficient chip evacuation, or excessive spindle speed cause the material to melt and re-weld behind the cutter — producing a gummy, opaque finish that requires extensive sanding. Use sharp two-flute upcut end mills, maintain aggressive feed rates (slow feed = more heat per tooth), and apply mist coolant. Critically, the coolant must be free of ammonia and aromatic compounds to avoid stress cracking on the machined surface.

For a deeper understanding of how surface finish specifications translate to functional performance, consult KUSLA Prototype’s surface roughness Ra and Rz guide.

7. Outdoor Weathering and Long-Term Durability

Outdoor performance is where acrylic and polycarbonate diverge most dramatically over time — and where the initial material cost comparison becomes misleading if replacement cycles are not factored in.

Acrylic Outdoor Performance

Cast acrylic sheet is one of the most weatherable engineering plastics available. Uncoated PMMA maintains >90% light transmission after 10 years of direct outdoor exposure in subtropical climates, with minimal yellowing or haze increase. This is why acrylic dominates in outdoor signage, aquarium panels, and architectural skylights where long-term optical clarity justifies the lack of impact resistance. Acrylic also resists salt spray well, making it suitable for marine and coastal environments.

Polycarbonate Outdoor Performance

Uncoated polycarbonate follows a predictable degradation curve outdoors: surface yellowing becomes visible within 2–3 years, accompanied by a progressive increase in haze and decrease in impact strength. After 5–7 years of unprotected outdoor exposure, polycarbonate sheets can lose up to 50% of their original impact resistance due to photodegradation of the polymer chain.

UV-coated polycarbonate (such as Makrolon UV or Lexan Margard grades) significantly extends this timeline to 10–15 years, but the coating is a surface treatment — CNC machining, drilling, or edge-finishing after coating removes the UV protection at cut edges, creating localized yellowing zones. Design for machinability before coating, or specify UV-stabilized mass-tinted grades for parts requiring post-machining.

8. Cost Breakdown: Sheet Price vs. Total Project Cost

Raw sheet cost comparisons are the most commonly cited — and most misleading — metric for material selection. While acrylic sheet stock costs approximately $1.50–$2.00/kg versus $2.50–$3.50/kg for polycarbonate (a 40–60% premium),⚠️ the total project cost equation includes machining, finishing, assembly, and lifecycle replacement.

Machining Cost Comparison

Acrylic typically machines faster than polycarbonate due to higher allowable feed rates and the ability to achieve optical-quality surface finish directly from the tool — eliminating post-polishing steps. For a typical prototyping batch of 10–50 parts, KUSLA Prototype estimates acrylic CNC parts cost 10–20% less than equivalent polycarbonate parts due to reduced cycle time and finishing labor.

However, acrylic’s brittleness increases scrap rates on complex geometries with thin walls or tight internal radii. Parts with wall sections below 1.5 mm or sharp internal corners are more likely to crack during machining, fixturing, or handling — each scrapped part adds material and machine-time cost. Polycarbonate’s ductility makes it forgiving of aggressive geometries, resulting in lower scrap rates on complex parts.

Total Cost of Ownership Framework

For indoor display, signage, and optical applications with no impact risk, acrylic delivers the lowest total cost. For safety glazing, enclosures, and applications where in-service breakage carries liability or downtime cost, polycarbonate’s higher material cost is offset many times over by reduced failure-related expenses.

9. Application Decision Matrix: Which Material Fits Your Project?

Use the following decision framework to select between polycarbonate and acrylic based on your project’s primary design criteria. Each row identifies the dominant requirement and the recommended material.