ABS and polycarbonate rank among the most commonly specified engineering thermoplastics for prototyping and low-volume production. Both materials machine well, injection mold predictably, and offer a favorable strength-to-cost ratio — but they solve different problems. ABS delivers dimensional stability and easy machinability at a lower price point. Polycarbonate provides superior impact resistance, optical clarity, and thermal performance at a premium.
This comparison covers the properties that actually drive material selection in CNC machining and injection molding projects: verified mechanical data, real-world machinability differences, processing parameters, cost modeling, and a DFM decision matrix. The goal is to help product designers and procurement engineers choose the right material before committing to tooling or cutting stock.
Scope boundary: This article compares general-purpose, unfilled ABS against standard unfilled polycarbonate (PC). For glass-filled or flame-retardant grades, consult grade-specific datasheets. For other engineering plastics like Delrin and nylon, see KUSLA’s Delrin vs Nylon comparison.
Mechanical & Thermal Properties: Side-by-Side Data
The following table compiles verified property ranges for general-purpose ABS and unfilled polycarbonate. All values are sourced from standardized ASTM test methods and cross-referenced against MatWeb, Curbell Plastics, and Protolabs published datasheets.
| Property | ABS (General Purpose) | Polycarbonate (Unfilled) | ASTM Method | Winner |
|---|---|---|---|---|
| Density | 1.04 g/cm³ | 1.20 g/cm³ | D792 | ABS (lighter) ABS |
| Tensile Strength (Yield) | 40–50 MPa | 55–72 MPa | D638 | PC PC |
| Elongation at Break | 30–40% | 50–100% | D638 | PC PC |
| Flexural Strength | 62–76 MPa | 86–96 MPa | D790 | PC PC |
| Flexural Modulus | 2.0–2.1 GPa | 2.1–2.5 GPa | D790 | PC PC |
| Notched Izod Impact | 200–410 J/m | 600–900 J/m | D256 | PC PC |
| HDT @ 1.8 MPa | 80–101°C | 128–138°C | D648 | PC PC |
| Rockwell Hardness | R100–R115 | M70–M75 (R118–R122) | D785 | Comparable |
| Water Absorption (24h) | 0.20–0.30% | 0.15–0.18% | D570 | PC PC |
| Glass Transition Temp (Tg) | ~105°C | ~147°C | — | PC PC |
✅ All values verified against at least two independent sources (MatWeb, Curbell Plastics, Protolabs).
What the Notched Izod Gap Really Means
The 2–3× difference in notched Izod impact between ABS (200–410 J/m) and PC (600–900 J/m) is the single largest performance gap in this comparison. Polycarbonate maintains impact resistance down to –40°C, while ABS drops sharply below 0°C. This cold-temperature impact retention is why PC dominates in automotive lens housings, outdoor enclosures, and safety equipment — applications where a –20°C winter morning could turn an ABS part brittle enough to crack on a minor drop.
At room temperature and above, ABS provides adequate impact resistance for most consumer electronics housings, toys, and appliance covers. The critical question is not “which is stronger” but “what impact load, at what temperature, does my part actually see in service?”
CNC Machinability: Cutting Behavior, Tolerances & Surface Finish
Both ABS and polycarbonate are among the easier engineering plastics to CNC machine, but they behave differently under the cutter. These differences affect cycle time, achievable tolerances, and post-machining cosmetic quality. KUSLA Prototype’s CNC machining service regularly processes both materials, and the machinability gap is noticeable in production.
| Machining Factor | ABS | Polycarbonate |
|---|---|---|
| Chip formation | Clean, short chips; easy evacuation | Stringy, continuous chips; requires air blast |
| Heat sensitivity | Moderate — softens above ~100°C at cut zone | Higher threshold (~147°C Tg), but stress-cracks if overheated |
| Stress cracking risk | Low | High — especially near drilled holes and sharp internal corners |
| Achievable tolerance (general) | ±0.10 mm | ±0.10 mm |
| Achievable tolerance (critical) | ±0.05 mm | ±0.05 mm (with annealing) |
| Surface finish (as-machined) | Smooth, matte; Ra 0.8–1.6 µm typical | Smooth but may show tool marks; Ra 0.4–1.6 µm |
| Post-machining polish | Rarely needed; vapor smoothing available | Often needed for optical parts; flame polishing possible |
| Coolant compatibility | Water-soluble OK; avoid aggressive solvents | Avoid alcohol-based coolants — causes crazing |
| Thin-wall risk threshold | 1.5 mm minimum wall | 2.0 mm minimum (stress-crack risk below 2 mm) |
The Stress-Cracking Problem with Machined Polycarbonate
Polycarbonate’s Achilles heel in CNC machining is stress cracking. Residual stresses from the cutting process can propagate micro-cracks, especially near drilled holes, tapped threads, and sharp internal corners. This is not a defect in the material — it is an inherent behavior of amorphous thermoplastics with high internal stress after machining.
KUSLA Prototype addresses this by annealing polycarbonate parts at 120–130°C for 1–4 hours after machining (depending on wall thickness), then slow-cooling at ≤10°C/hour. This step adds cycle time and cost, but eliminates the majority of delayed cracking failures. For ABS, annealing is almost never required — another reason ABS wins on total cost for geometries that do not require PC’s mechanical performance.
Injection Molding: Shrinkage, Processing & Mold Design Differences
Material selection affects not just part performance but mold design, cycle time, and per-unit economics. The processing window differences between ABS and polycarbonate create downstream cost implications that many comparison guides ignore.
| Processing Parameter | ABS | Polycarbonate |
|---|---|---|
| Melt temperature range | 220–260°C | 280–320°C |
| Mold temperature | 40–80°C | 80–120°C |
| Mold shrinkage | 0.4–0.9% | 0.5–0.7% |
| Drying requirement | 2–4 hrs @ 80°C | 3–4 hrs @ 120°C |
| Injection pressure | 50–100 MPa | 80–150 MPa |
| Cycle time (3 mm wall, same geometry) | Baseline | 15–25% longer |
| Gate sensitivity | Low — tolerates most gate types | Higher — requires larger gates for flow |
| Weld line strength | 70–80% of base | 80–90% of base |
Shrinkage Predictability: Why PC Is Easier to Hold Tolerances
Polycarbonate’s tighter shrinkage range (0.5–0.7%) compared to ABS (0.4–0.9%) means less dimensional variation between first articles and production runs. For parts with critical fits or mating surfaces, PC’s predictable shrinkage reduces the risk of costly mold adjustments after T1 sampling. The trade-off is higher mold temperatures and injection pressures, which may require upgrading mold steel or adding cooling channels.
Tooling Cost Impact
Polycarbonate’s higher processing temperature (280–320°C vs 220–260°C for ABS) means molds need heat-treated steel (H13 or equivalent) for long production runs. ABS can run in P20 pre-hardened steel molds for volumes up to 100,000–500,000 shots before significant wear. This tooling steel difference can add $2,000–$5,000 to a single-cavity mold cost — a factor that matters in low-to-medium volume production where amortization is limited.
Chemical Resistance & Environmental Durability
Chemical resistance is an often-overlooked selection criterion. Both materials are amorphous thermoplastics, making them inherently less chemically resistant than semi-crystalline alternatives like Delrin or nylon. However, their failure modes differ significantly.
| Chemical/Environment | ABS | Polycarbonate |
|---|---|---|
| Dilute acids | Good | Good |
| Dilute alkalis | Good | Fair — surface hazing possible |
| Alcohols (IPA, ethanol) | Good | ⚠️ Poor — causes stress cracking |
| Ketones (acetone, MEK) | ⚠️ Poor — dissolves/softens | ⚠️ Poor — attacks surface |
| Aromatic hydrocarbons | Poor | Poor |
| UV exposure (unprotected) | Poor — yellows, becomes brittle | Fair — yellows slowly, retains strength longer |
| Outdoor weathering (5+ years) | Not recommended without UV stabilizer | Requires UV-stabilized grade or coating |
| Hydrolysis resistance | Good | ⚠️ Moderate — degrades in sustained hot/humid conditions |
Optical Properties & Aesthetic Considerations
Optical performance is the one dimension where polycarbonate has no ABS equivalent. This is not a matter of degree — it is a binary capability gap.
Polycarbonate transmits 88–90% of visible light in its natural (unfilled) state, making it suitable for lenses, light guides, display windows, and transparent enclosures. ABS is inherently opaque. No amount of processing or additive modification makes ABS transparent.
Surface Finish & Color Matching
For opaque parts, ABS offers superior aesthetic versatility. It accepts painting, plating (chrome, nickel), pad printing, and hot stamping with minimal surface preparation. ABS’s matte, uniform surface texture hides minor molding imperfections better than PC.
Polycarbonate can be painted and printed, but its natural transparency means any sub-surface defect (voids, flow lines, splay marks) is visible. Opaque PC parts require either pigment loading or post-mold painting, adding cost compared to pre-colored ABS pellets.
For scratch resistance in visible surfaces, ABS outperforms uncoated polycarbonate. PC scratches easily and typically requires a hard-coat treatment (silicone-based or UV-cured) for consumer-facing applications — another post-process cost to factor in.
Cost Modeling: Raw Material, Machining & Tooling Economics
Raw material cost alone is a misleading basis for material selection. The total manufactured cost includes material, machining or molding cycle time, post-processing, tooling life, and scrap rate. This section breaks down each component.
| Cost Factor | ABS | Polycarbonate | PC Premium |
|---|---|---|---|
| Resin/pellet cost | ~$0.90/kg | ~$1.50/kg | ~67% more |
| CNC rod/sheet stock | Baseline | 40–60% more | Varies by supplier |
| CNC cycle time (same geometry) | Baseline | 5–15% longer (slower feeds near edges) | — |
| Post-CNC annealing | Rarely needed | Often required (adds 2–8 hrs) | $15–50/batch |
| Injection mold steel | P20 (pre-hardened) | H13 (heat-treated) for >50K shots | $2,000–5,000/mold |
| Injection cycle time | Baseline | 15–25% longer | — |
| Scrap rate (CNC) | Low (2–5%) | Higher (5–10% — stress-crack rejects) | — |
⚠️ Cost data is market-variable. Resin prices fluctuate with petrochemical feedstock markets. The figures above represent 2025–2026 North American averages and should be confirmed with current supplier quotes.
Break-Even Analysis: When Does PC’s Premium Pay for Itself?
Polycarbonate’s higher material and processing costs are justified when the alternative is a more expensive downstream solution. Common scenarios where PC pays for itself:
- Eliminating a separate lens or window: A transparent PC housing replaces an opaque ABS housing + bonded acrylic window, saving assembly labor and a seal failure point.
- Avoiding over-design in ABS: When ABS requires 3 mm walls to survive a 1-meter drop test, PC may achieve the same result at 2 mm — saving material and cycle time that offsets the resin premium.
- Reducing field failure costs: For outdoor or cold-environment products, ABS’s brittle failure mode below 0°C can generate warranty claims that dwarf the material cost difference.
DFM Decision Matrix: When to Choose Which
The following decision matrix maps common design requirements to recommended material choices. This is KUSLA Prototype’s internal framework used during DFM review — a tool that consolidates the property, machinability, and cost data above into actionable selection logic.
Material Selection Decision Matrix
| Design Requirement | ABS | PC | PC/ABS Blend | Rationale |
|---|---|---|---|---|
| Transparency required | ❌ | ✅ | ❌ | PC is the only option among these three |
| Operating temp >100°C | ❌ | ✅ | ✅ | ABS HDT too low; PC and blend both qualify |
| Drop test: 1m onto concrete, –20°C | ❌ | ✅ | ✅ | ABS impact drops sharply below 0°C |
| Regular alcohol/IPA wipe-down | ✅ | ❌ | ⚠️ | PC stress-cracks with alcohol exposure |
| Chrome plating required | ✅ | ❌ | ⚠️ | ABS is the standard substrate for decorative plating |
| Budget-constrained prototype (<10 pcs) | ✅ | ⚠️ | ⚠️ | ABS is cheaper to machine and buy in small quantities |
| Thin walls <1.5 mm | ⚠️ | ✅ | ✅ | PC’s ductility handles thin sections better |
| UL94 V-0 flame rating needed | ⚠️ | ✅ | ✅ | Standard PC is inherently V-2; V-0 grades available. ABS requires FR additives |
| High-volume (>100K units), opaque | ✅ | ❌ | ⚠️ | ABS’s lower resin cost and faster cycle times compound at volume |
| Outdoor, unshielded UV exposure | ❌ | ⚠️ | ⚠️ | Neither is ideal; ASA or UV-stabilized PC preferred |
✅ = recommended, ⚠️ = possible with caveats, ❌ = not recommended
PC/ABS Blends: The Third Option Most Comparisons Miss
A significant gap in most ABS-vs-polycarbonate comparisons is the omission of PC/ABS blends — engineered alloys that combine the processability and chemical resistance of ABS with the impact strength and heat resistance of polycarbonate. These blends account for a substantial share of automotive interior and consumer electronics housings, yet rarely appear in material comparison articles.
| Property | ABS | PC/ABS Blend | PC |
|---|---|---|---|
| Tensile Strength | 40–50 MPa | 41–55 MPa | 55–72 MPa |
| Notched Izod Impact | 200–410 J/m | 480–640 J/m | 600–900 J/m |
| HDT @ 1.8 MPa | 80–101°C | 100–115°C | 128–138°C |
| Alcohol resistance | Good | Moderate (better than PC) | Poor |
| Resin cost | ~$0.90/kg | ~$1.10–1.30/kg | ~$1.50/kg |
| Melt temp range | 220–260°C | 240–280°C | 280–320°C |
PC/ABS blends are particularly effective for laptop housings, automotive pillar trims, power tool casings, and telecom equipment enclosures — applications that need more impact than ABS provides but do not require PC’s full transparency or thermal ceiling.
Application Mapping by Industry
Rather than listing generic applications, the following maps material choices to specific industry requirements and explains why each material wins in that context.
| Industry / Application | Recommended | Why |
|---|---|---|
| Consumer electronics housings (phones, remotes, controllers) | ABS | Cost-effective, excellent platability, adequate impact at room temp |
| Automotive headlamp lenses | PC | Optical clarity + thermal resistance from bulb heat + cold-impact survival |
| Safety helmets / face shields | PC | Impact resistance per ANSI Z87.1; cold-temp ductility |
| LEGO-style toys / snap-fit assemblies | ABS | Dimensional stability, consistent snap-fit retention, low cost |
| Medical device housings (disinfected with IPA) | ABS | Alcohol resistance; PC would stress-crack |
| Outdoor telecom enclosures | PC | UV-stabilized grades + impact at –40°C + flame retardancy |
| Rapid prototyping (functional fit-check) | ABS | Cheapest machining stock, fastest cycle time, easy to modify |
| LED light diffusers / light guides | PC | 88–90% light transmission, thermoformable, shatter-resistant |
| Laptop / tablet housings | PC/ABS | Blend delivers thin-wall impact + paintability + lower cost than pure PC |
For projects that span multiple material requirements, KUSLA Prototype offers material selection consulting as part of the DFM review process. The engineering team evaluates application loads, environment, regulatory requirements, and production volume before recommending a final material specification.
Related KUSLA Guides
- Delrin vs Nylon: Engineering Plastic Comparison — another key material pairing for CNC machined parts
- CNC Milling vs Turning: Process Selection Guide — choosing the right machining process for your plastic parts
- KUSLA Materials Hub — complete material library with specifications and DFM guidance
- CNC Machining Services — prototyping and production capabilities for ABS, PC, and 50+ engineering materials
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