Plastic Materials — Appendix & Reference Data
Last updated: May 23, 2026
Plastic Materials — Appendix & Reference Data
← Back to the Plastic Materials Handbook
Rating legend — ★★★★★ best · ★☆☆☆☆ worst. For machinability, wear, heat resistance, and chemical resistance, more stars = better; for cost, fewer stars = cheaper.
1. Master Material Property Comparison Table ⭐⭐⭐⭐⭐
This is the master comparison table for CNC-machined plastic materials in this handbook. Values are typical reference ranges for common unfilled grades unless noted. Actual data varies by grade, filler content, moisture condition, supplier, color, and test method.
| Material | Density (g/cm³) | Tensile Strength (MPa) | Max Continuous Temp (℃) | Machinability (★) | Cost (★, fewer=cheaper) | Key Characteristics |
|---|---|---|---|---|---|---|
| PMMA / Acrylic | 1.17~1.20 | 60~80 | 70~90 | ★★★★☆ | ★★☆☆☆ | Excellent optical clarity, high gloss, easy polishing, good weatherability; brittle and notch-sensitive |
| ABS | 1.03~1.07 | 35~50 | 70~85 | ★★★★☆ | ★★☆☆☆ | Low-cost engineering plastic, tough, easy to machine, paint, bond, and plate; moderate heat and chemical resistance |
| PP / Polypropylene | 0.90~0.91 | 25~35 | 90~110 | ★★★☆☆ | ★☆☆☆☆ | Very low density, excellent chemical resistance, fatigue-resistant living hinges; flexible and prone to burrs |
| PE / HDPE / UHMW-PE | 0.93~0.97 | 20~45 | 80~100 | ★★★☆☆ | ★★☆☆☆ | Low friction, high impact toughness, good chemical resistance; UHMW-PE is wear-resistant but gummy to machine |
| PVC / Rigid PVC | 1.35~1.45 | 40~60 | 60~80 | ★★★★☆ | ★★☆☆☆ | Chemical-resistant, rigid, low-cost, naturally flame-retardant; poor high-temperature safety due to HCl release |
| POM / Acetal | 1.41~1.42 | 60~70 | 90~110 | ★★★★★ | ★★★☆☆ | Best all-round machinability, low friction, high dimensional stability, excellent gear and bearing material |
| PA / Nylon | 1.13~1.15 | 60~90 | 90~120 | ★★★★☆ | ★★★☆☆ | Tough, wear-resistant, fatigue-resistant; absorbs moisture, so precision parts need moisture control and conditioning |
| PC / Polycarbonate | 1.19~1.22 | 60~70 | 115~125 | ★★★☆☆ | ★★★☆☆ | Transparent, extremely impact-resistant, good heat resistance; stress cracking and internal stress require care |
| PET / PET-P | 1.37~1.39 | 55~80 | 100~115 | ★★★★☆ | ★★★☆☆ | Dimensionally stable, low moisture absorption, good wear resistance, food-grade options; less tough than nylon |
| PEEK | 1.30~1.32 | 90~100 | 240~260 | ★★★★☆ | ★★★★★ | High-temperature, high-strength, chemical-resistant, medical/aerospace grade options; expensive but metal-replacement capable |
| PTFE / Teflon | 2.13~2.20 | 20~35 | 260 | ★★☆☆☆ | ★★★★☆ | Best chemical resistance, ultra-low friction, excellent insulation; soft, creeps easily, difficult to hold tight tolerances |
| PEI / Ultem | 1.27~1.28 | 100~120 | 170~180 | ★★★☆☆ | ★★★★☆ | High-strength amorphous plastic, flame-smoke-toxicity performance, good dimensional stability; stress-sensitive |
| PI / Polyimide | 1.42~1.43 | 100~230 | 260~300 | ★★★☆☆ | ★★★★★ | Extreme heat resistance, high strength at temperature, excellent wear grades; very expensive and often abrasive |
| PSU / PPSU | 1.24~1.30 | 70~85 | 150~180 | ★★★☆☆ | ★★★★☆ | Transparent amber high-temperature polymers, hydrolysis/steam sterilization resistance, medical and electrical use |
| PPS | 1.34~1.36 | 65~90 | 200~220 | ★★★☆☆ | ★★★★☆ | High heat and chemical resistance, inherently flame-retardant, dimensionally stable; filled grades are abrasive |
📌 How to use this table: start with the required operating environment (temperature, load, chemicals, transparency, wear), then check machinability and cost. For tight-tolerance CNC work, dimensional stability and stress relief are often as important as headline strength.
2. Material Selection Quick Reference
| Requirement / Design Goal | Recommended Materials | Practical Notes |
|---|---|---|
| Transparency / optical parts | PMMA, PC | PMMA gives the best polish and optical clarity; PC gives much higher impact resistance |
| Wear parts, gears, bearings, sliders | POM, PA, UHMW-PE, PET | POM is the default precision gear material; PA is tougher; UHMW-PE is excellent for sliding wear but less precise |
| High temperature resistance | PEEK, PI, PTFE, PPS | PEEK is the balanced high-performance option; PI is for extreme heat; PTFE is chemically inert but weak mechanically |
| Corrosion / chemical resistance | PTFE, PP, PVC, PVDF | PTFE is the safest chemical-resistance choice; PP/PVC are economical; PVDF is a specialty option for higher-performance chemical service |
| Electrical insulation | PTFE, PEI, PVC | PTFE has outstanding dielectric properties; PEI adds heat and flame performance; PVC is economical |
| High-strength metal replacement | PEEK, PEI, PI | Check creep, temperature, fatigue, and fastening design; plastics still have much lower modulus than metals |
| Low-cost prototyping | ABS, PMMA | ABS is forgiving and easy to finish; PMMA is ideal when appearance and transparency matter |
| Medical / sterilizable parts | PEEK, PSU/PPSU | Confirm biocompatibility, USP/ISO grade, sterilization method, and lot traceability with the supplier |
| FST / aerospace interior needs | PEI, PEEK | Use certified grades; flame, smoke, toxicity, and traceability requirements are application-specific |
💡 Default choices: if no extreme requirement exists, start with POM for precision mechanical parts, ABS for low-cost prototypes, PMMA/PC for clear parts, PP/PVC/PTFE for chemicals, and PEEK/PEI/PI for high-performance service.
3. Rating System Explained
The handbook uses a five-star scale to help compare materials quickly. Ratings are practical CNC selection indicators, not formal standards.
| Rating | Meaning |
|---|---|
| ★★★★★ | Excellent / top-tier performance in this category |
| ★★★★☆ | Very good, commonly suitable for demanding work |
| ★★★☆☆ | Moderate / acceptable with normal design precautions |
| ★★☆☆☆ | Limited, requires careful process or design control |
| ★☆☆☆☆ | Poor / use only when other properties dominate the selection |
3.1 Machinability Rating
| Machinability | Practical Meaning |
|---|---|
| ★★★★★ | Cuts cleanly, stable dimensions, good finish, low burrs; ideal CNC plastic |
| ★★★★☆ | Easy to machine with sharp tools and normal chip control |
| ★★★☆☆ | Machinable but sensitive to heat, stress, burrs, or tool geometry |
| ★★☆☆☆ | Difficult due to softness, creep, high thermal expansion, or poor chip breaking |
| ★☆☆☆☆ | Generally unsuitable for precision CNC unless special fixtures/processes are used |
3.2 Wear Rating
More stars indicate better performance for sliding, gears, bushings, rollers, and repeated motion.
- ★★★★★: excellent low-friction or self-lubricating behavior, e.g. POM, selected PA/UHMW-PE/PTFE grades
- ★★★☆☆: usable for moderate wear if loads and speeds are controlled
- ★☆☆☆☆: not recommended for moving wear parts
3.3 Heat Rating
More stars indicate better continuous service at elevated temperature.
- ★★★★★: high-performance polymers such as PEEK, PI, PTFE, PPS
- ★★★☆☆: engineering plastics such as PC, PA, PET, POM
- ★☆☆☆☆: commodity plastics or low-HDT grades exposed to load and heat
3.4 Chemical Rating
More stars indicate broader resistance to acids, bases, solvents, fuels, cleaning agents, and industrial fluids.
⚠️ Chemical compatibility is highly concentration- and temperature-dependent. Always confirm with a chemical compatibility chart and real exposure testing.
3.5 Cost Rating ⭐ Important
For cost only, the scale is inverted:
| Cost Rating | Meaning |
|---|---|
| ★☆☆☆☆ | Cheapest / commodity material |
| ★★☆☆☆ | Low cost |
| ★★★☆☆ | Moderate cost engineering plastic |
| ★★★★☆ | Expensive high-performance plastic |
| ★★★★★ | Very expensive specialty polymer |
📌 Fewer cost stars = cheaper. This convention is used throughout the handbook.
4. Unit Conversion Tables
The handbook primarily uses metric units. Use the following tables for common imperial conversions.
4.1 Length
| Metric | Imperial | Notes |
|---|---|---|
| 1 mm | 0.03937 in | 1 inch = 25.4 mm exactly |
| 10 mm | 0.3937 in | Approx. 3/8 in |
| 25.4 mm | 1.000 in | Exact inch conversion |
| 100 mm | 3.937 in | Approx. 4 in |
| 1 m | 39.37 in / 3.281 ft | 1000 mm |
4.2 Temperature
Formula:
℉ = ℃ × 9/5 + 32
℃ = (℉ - 32) × 5/9
| ℃ | ℉ | Common Meaning |
|---|---|---|
| -40 | -40 | Low-temperature service benchmark |
| 0 | 32 | Water freezing point |
| 20 | 68 | Room-temperature reference |
| 80 | 176 | Typical upper limit for many low-cost plastics |
| 100 | 212 | Water boiling point at 1 atm |
| 150 | 302 | High for many engineering plastics |
| 200 | 392 | High-performance polymer range |
| 260 | 500 | PTFE/PEEK/PI-class reference temperature |
⚠️ HDT is not the same as continuous service temperature. HDT is measured under a specified load; continuous service temperature depends on load, environment, exposure time, and safety factor.
4.3 Pressure / Strength
| MPa | psi | ksi |
|---|---|---|
| 1 | 145 | 0.145 |
| 10 | 1,450 | 1.45 |
| 25 | 3,626 | 3.63 |
| 50 | 7,252 | 7.25 |
| 75 | 10,878 | 10.88 |
| 100 | 14,504 | 14.50 |
| 200 | 29,008 | 29.01 |
Quick conversion: 1 MPa = 145.038 psi = 0.145 ksi.
4.4 Density
| g/cm³ | lb/in³ | Typical Material Example |
|---|---|---|
| 0.90 | 0.0325 | PP |
| 0.95 | 0.0343 | PE / HDPE |
| 1.20 | 0.0434 | PMMA / PC |
| 1.40 | 0.0506 | POM / PET / PVC range |
| 2.20 | 0.0795 | PTFE |
Quick conversion: 1 g/cm³ = 0.03613 lb/in³.
4.5 Hardness Scale Note
| Scale | Common Use | Important Note |
|---|---|---|
| Rockwell M | Hard engineering plastics such as POM, PMMA, PC, PA | Useful for rigid plastics; not directly convertible to Shore D |
| Rockwell R | Softer rigid plastics and semi-rigid plastics | Common on ABS, PVC, and similar materials |
| Shore D | General plastics hardness, including softer engineering plastics | Indentation method differs from Rockwell; conversion is approximate only |
📌 Hardness scales are not directly interchangeable. Rockwell M/R and Shore D use different indenters, loads, and measurement methods. Use supplier datasheets and the same test method when comparing grades.
5. Glossary of Terms
| Term | Definition |
|---|---|
| Amorphous vs semi-crystalline | Amorphous plastics have a random molecular structure and often better transparency; semi-crystalline plastics have ordered crystalline regions, often improving chemical resistance, wear, and fatigue behavior. |
| Annealing | Controlled heating and slow cooling to reduce internal stress, improve dimensional stability, and reduce warping after machining. |
| Climb milling | Milling method where cutter rotation pulls the tool into the workpiece. Often gives better finish but requires rigid fixturing and backlash-free machines. |
| Creep / cold flow | Permanent deformation under sustained load, even below the material’s yield strength. PTFE and PE are especially creep-sensitive. |
| Crazing | Fine surface cracking or whitening caused by stress, solvents, or environmental exposure; common concern for PMMA and PC. |
| CTE (coefficient of thermal expansion) | Rate of dimensional change with temperature. Plastics usually expand far more than metals, affecting tolerances and fits. |
| HDT (heat deflection temperature) | Temperature at which a test specimen deflects under a specified load. Useful for comparison, but not equal to maximum service temperature. |
| Hygroscopic | Tendency to absorb moisture from air or water. Nylon is hygroscopic and may change size and properties with moisture content. |
| Machinability | Practical ease of CNC cutting, including chip formation, burr control, heat sensitivity, achievable tolerance, and surface finish. |
| Notch sensitivity | Tendency to crack or fail from sharp corners, scratches, threads, or grooves. Use generous radii and avoid sharp internal corners. |
| Outgassing | Release of trapped gases, moisture, or volatiles, especially under vacuum or heat. Important for aerospace, optics, semiconductor, and vacuum equipment. |
| Rake angle | Tool cutting-edge angle that affects cutting force, chip flow, heat generation, and surface finish. Plastics generally prefer sharp tools with positive rake. |
| Self-lubricating | Ability to slide with low friction without added lubricant. POM, PTFE, UHMW-PE, and some filled grades are common examples. |
| Stress relief | Process or design practice that reduces residual stress from extrusion, molding, machining, or clamping. Annealing is a common stress-relief method. |
| Tg (glass transition temperature) | Temperature where amorphous regions soften from glassy to rubbery behavior. Above Tg, stiffness and dimensional stability decrease sharply. |
| UL94 (flammability rating) | Standardized plastic flammability classification such as HB, V-2, V-1, and V-0. V-0 is more flame-retardant than HB. |
| Water absorption | Amount of water a plastic absorbs under specified test conditions. High absorption can change dimensions, strength, and electrical properties. |
6. General Safety Notes (All Plastics) ⚠️
Plastic CNC machining is generally safe when heat, dust, and chip control are managed correctly. The major hazards are fine dust inhalation, combustible dust, thermal decomposition fumes, static buildup, and material-specific decomposition products.
6.1 Universal Machining Safety Checklist
| Safety Item | Requirement |
|---|---|
| Dust inhalation | Use local extraction or vacuum collection, especially during dry machining, routing, sanding, and deburring. Wear a suitable mask/respirator when dust exposure is possible. |
| Combustible dust | Avoid dust accumulation around machines, electrical cabinets, motors, and hot surfaces. Fine plastic dust can burn rapidly when dispersed in air. |
| Ventilation / extraction | Provide strong ventilation when machining, drilling, engraving, or cutting plastics that may overheat. Never allow plastic to smoke or smolder in the cut. |
| Chip control | Use sharp tools, correct feed, air blast, vacuum, or coolant where appropriate. Poor chip evacuation increases heat and fume risk. |
| PPE | Wear eye protection, appropriate respiratory protection for dust, and gloves when handling sharp chips or stock. Do not wear loose gloves near rotating spindles. |
| Heat control | Plastics have low thermal conductivity. Dull tools and rubbing cuts can melt material, damage tolerance, and release fumes. |
| Coolant compatibility | Confirm coolant compatibility with the material. Some plastics stress-crack or swell in contact with oils, solvents, or aggressive cleaners. |
| Fire control | Keep chips and dust away from open flames, welding, heaters, and sparks. Know whether the material self-extinguishes or drips while burning. |
6.2 Material-Specific Hazard Summary
| Material / Grade | Main Hazard | Precaution |
|---|---|---|
| PVC | Overheating or burning can release hydrogen chloride (HCl) and other corrosive chlorine-containing fumes | Avoid high heat, smoking cuts, laser cutting without proper controls, and poor ventilation; protect machine surfaces from corrosive fumes |
| PTFE | Overheating can release highly toxic decomposition fumes; inhalation may cause polymer fume fever | Keep cutting cool, use sharp tools, avoid thermal processes unless professionally controlled, and provide excellent ventilation |
| POM / Acetal | Thermal decomposition can release formaldehyde gas | Prevent smoldering and rubbing cuts; use sharp tools, chip evacuation, and extraction |
| Filled grades | Glass fiber, carbon fiber, mineral, or PTFE-filled materials may produce abrasive and irritating dust | Use extraction, respirator when needed, and abrasion-resistant tooling; protect guideways and clean machines carefully |
⚠️ Do not rely on smell as a safety control. Some decomposition products are hazardous before odor becomes obvious, and dust exposure can be harmful even when no fumes are present.
6.3 Flammability & Dripping
| Issue | Note |
|---|---|
| Flame rating varies by grade | A base polymer may be HB while a flame-retardant grade may be V-0. Always check the exact datasheet. |
| Burning droplets | Some plastics melt and drip while burning, spreading fire risk. POM and many commodity plastics can drip. |
| Halogenated fumes | PVC and some flame-retardant grades can release corrosive/toxic gases when burned. |
| High-performance does not mean non-combustible | PEEK, PEI, PPS, and PI perform better than commodity plastics, but still require grade-specific fire evaluation. |
6.4 Static / ESD
Plastic chips and dust can build static charge during dry machining.
- Use grounded extraction hoses and dust collectors where appropriate.
- Use ESD-safe material grades for electronics fixtures, semiconductor tooling, and sensitive assembly areas.
- Avoid uncontrolled dust clouds near ignition sources.
6.5 Storage Notes
| Storage Concern | Recommendation |
|---|---|
| Moisture | Keep hygroscopic plastics, especially PA / Nylon, dry and conditioned according to machining/tolerance requirements. |
| UV exposure | Store UV-sensitive materials indoors or covered. PMMA has good weatherability, but many plastics degrade under prolonged UV without stabilizers. |
| Flatness | Store sheets flat and supported to avoid warping. Avoid leaning thin plates for long periods. |
| Contamination | Keep medical, food, optical, or electrical grades clean and separated by lot when traceability matters. |
6.6 PPE Reminder ✅
| PPE | Use Case |
|---|---|
| Safety glasses / face shield | Required for flying chips, brittle plastics, drilling, routing, and deburring |
| Dust mask / respirator | Use during dusty cutting, sanding, engraving, or filled-grade machining |
| Gloves | Use for handling raw stock and sharp chips; avoid loose gloves near rotating tools |
| Hearing protection | Use when routing, high-speed milling, vacuum extraction, or air blast noise is high |
7. Standards Reference
Material datasheets often use ISO, ASTM, UL, and supplier-specific test methods. The following are common references for CNC plastic material comparison.
| Standard / Method | What It Measures | Notes |
|---|---|---|
| ISO material standards | General plastics properties and test methods | Widely used internationally; compare only when test conditions match |
| ASTM D638 | Tensile properties | Tensile strength, elongation, and tensile modulus for plastics |
| ASTM D790 | Flexural properties | Flexural strength and flexural modulus under bending load |
| ASTM D648 | Heat deflection temperature (HDT) | Measures deflection under load at elevated temperature; not the same as continuous service temperature |
| UL94 | Flammability classification | Common ratings include HB, V-2, V-1, and V-0; grade thickness affects rating |
📌 Datasheet values vary. Grade, fillers, colorants, processing history, moisture content, test temperature, specimen thickness, and supplier method can all change reported values. For critical parts, request the exact grade datasheet and validate by prototype testing.