Plastic resin identification.
The seven recycling codes plus common engineering plastics — chemical name, typical uses, temperature range, and recycling implications. From PET water bottles to PEEK gears.
The chart
| Code | Resin | Common uses | Max temp | Notes |
|---|---|---|---|---|
| 1 — PET / PETE | Polyethylene terephthalate | Water bottles, soda bottles, food packaging, polyester fiber | 60 °C (140 °F) | Recyclable. Most common single-use bottle. Don't reuse — leaches at warm temps. |
| 2 — HDPE | High-density polyethylene | Milk jugs, detergent bottles, pipes, plastic bags, lumber | 120 °C (248 °F) | Recyclable. Stiffer than LDPE. Resistant to most chemicals. |
| 3 — PVC / V | Polyvinyl chloride | Pipes (rigid), wire insulation, flooring, medical tubing | 60-80 °C (140-176 °F) | Hard to recycle. Contains chlorine — releases toxic fumes when burned. |
| 4 — LDPE | Low-density polyethylene | Plastic bags, squeeze bottles, film, food wrap | 80 °C (176 °F) | Sometimes recyclable. Softer, flexible. Food-safe. |
| 5 — PP | Polypropylene | Yogurt containers, bottle caps, automotive parts, fibers | 120 °C (248 °F) | Microwave-safe. Generally regarded as safe; better recyclability than 3 or 6. |
| 6 — PS | Polystyrene | Disposable cups, foam packaging, CD cases, plastic cutlery | 70-90 °C (158-194 °F) | Hard to recycle. Brittle. Styrofoam is expanded PS — banned in some cities. |
| 7 — Other / O | Mixed / specialty (PC, ABS, nylon, etc.) | Multi-resin laminates, BPA-containing plastics, specialty parts | Varies widely | Usually NOT recyclable curbside. Includes engineering plastics. |
| ABS | Acrylonitrile butadiene styrene | LEGO, automotive trim, 3D printing, electronic housings | 80 °C (176 °F) | Tough, machinable. The default 3D printing filament alongside PLA. |
| PC | Polycarbonate | Eyeglass lenses, safety shields, CD/DVD discs, baby bottles (old) | 120 °C (248 °F) | Strong, transparent. BPA controversy — many countries restrict PC for food/baby use. |
| Acetal / POM (Delrin) | Polyoxymethylene | Gears, bearings, machined parts, precision mechanical | 100 °C (212 °F) | Self-lubricating. Excellent machinability. Engineering plastic. |
| Nylon (PA) | Polyamide (Nylon 6, 6/6, 11, 12) | Gears, bushings, cable ties, textiles, fishing line | 100-150 °C (212-302 °F) | Tough, abrasion-resistant. Absorbs water — changes dimensions slightly with humidity. |
| PMMA (Acrylic / Plexiglass) | Polymethyl methacrylate | Aquariums, signs, optical lenses, displays | 80 °C (176 °F) | Transparent like glass, easier to machine. UV stable. Brittle vs PC. |
| PTFE (Teflon) | Polytetrafluoroethylene | Non-stick cookware, chemical seals, plumbing tape, gaskets | 260 °C (500 °F) | Extremely chemically resistant. Releases toxic fumes only above 350 °C. |
| PLA | Polylactic acid | 3D printing (standard filament), biodegradable packaging | 60 °C (140 °F) | Biodegradable (industrial composting). Low temperature limit makes it unsuitable for hot environments. |
| PEEK | Polyetheretherketone | Aerospace, medical implants, oil & gas seals, high-temp gears | 250 °C (482 °F) | High-temperature engineering plastic. Very expensive. Mechanical properties approach some metals. |
About the recycling code. The chasing-arrow symbol with a number inside (1-7) is the Resin Identification Code, established by SPI in 1988. It identifies the resin — it does NOT mean the plastic is recyclable in your area. Local recycling varies wildly: most curbside programs accept 1 and 2; few accept 3, 6, or 7. Confirm with your local waste management.
Common applications
| Use case | Recommended plastic | Why |
|---|---|---|
| 3D printing — beginner | PLA | Low warp, easy to print, biodegradable |
| 3D printing — durable | PETG or ABS | Tougher than PLA, higher temp resistance |
| 3D printing — engineering | Nylon, PC, PEEK | Best mechanical properties |
| Outdoor / UV exposure | HDPE, ABS, PC | UV-stable. PVC + LDPE degrade in sun. |
| Food / drink containers | PP, HDPE, PET | Non-leaching. Avoid PC (BPA), PS (styrene). |
| Microwave-safe container | PP | Highest temperature tolerance among common food plastics |
| Machined gears or bearings | Acetal (Delrin), Nylon, PTFE | Self-lubricating, dimensionally stable |
| Chemical / acid resistance | PTFE, HDPE, PP | PTFE for severe; HDPE for moderate |
| Clear / optical | PMMA (acrylic) or PC | PMMA for UV; PC for impact |
| High temperature (>150 °C) | PTFE, PEEK, PI | Standard plastics deform |
Common pitfalls
- Recycling symbol ≠ recyclable. The number tells you the resin. It does NOT mean your recycler accepts it. Most communities accept only 1 and 2 from curbside collection. Some specialty programs accept others.
- 'BPA-free' doesn't mean safer. Many 'BPA-free' replacements use BPS or BPF — chemically similar with similar concerns. The safest food contact plastics for hot use are PP (5) and silicone (not coded — it's not a plastic in this sense).
- Plastics degrade in sunlight (UV) and heat. Don't expect outdoor longevity from indoor-rated plastics. Black plastics (with carbon black additive) last much longer outdoors than clear ones because carbon absorbs UV.
- Plastic IDs aren't unique. Two products both marked '5 / PP' may have very different additives, fillers, and impact modifiers, leading to very different properties. The code identifies the base polymer only.
- Nylon and PA absorb water. Nylon 6 can absorb up to 10% of its weight in water at equilibrium with humid air, causing it to swell ~3% and lose stiffness. For dimensional stability, use moisture-stable nylon grades (PA 12) or alternatives (acetal).
- Thermoset vs thermoplastic isn't shown. All resins in this chart are thermoplastics — they can be remelted. Thermosets (epoxy, polyester, vulcanized rubber) once cured can't be remelted and aren't typically labeled with these codes.
Common questions
What do the recycling numbers mean?
Numbers 1-7 inside the recycling triangle identify the plastic resin. 1 = PET (water bottles), 2 = HDPE (milk jugs), 3 = PVC (pipes), 4 = LDPE (plastic bags), 5 = PP (yogurt containers), 6 = PS (foam), 7 = Other (PC, PLA, mixed). They don't mean the plastic IS recyclable in your area — they just identify the material.
Is PLA actually biodegradable?
Only under industrial composting conditions: 50-60°C, controlled humidity, microbial environment. In a backyard compost or landfill, PLA can persist for decades — similar to other plastics. So '100% biodegradable' on a PLA cup is technically true only if you ship it to an industrial composter, which most municipalities don't accept.
Which plastics are food-safe?
PET, HDPE, LDPE, and PP are FDA-approved for food contact. PVC and PS are food-safe in some forms but can leach plasticizers under heat or with oily foods — avoid for hot or fatty foods. PC contains BPA and is generally avoided for food storage. PLA is food-safe and increasingly common in disposable cups.
Why does ABS smell when 3D printed?
ABS releases styrene and other volatile organic compounds when heated to printing temperature (220-250°C). The smell isn't just unpleasant — sustained exposure has health implications. Print ABS in a ventilated area or enclosed printer with filtered exhaust. PLA prints with much less fume and is the safer hobby option.
What plastic can I use for high temperatures?
For continuous exposure above 100°C, you need engineered plastics: PEEK (260°C), PPS (220°C), PTFE/Teflon (260°C), or fiberglass-reinforced PA (130°C). Consumer plastics like PP and HDPE soften above 100-120°C. For hot food applications (dishwasher, microwave), PP is OK; for boiling oil or steam, you need engineered grades.
Sources
- Resin identification codes: ASTM D7611 — Standard Practice for Coding Plastic Manufactured Articles for Resin Identification.
- Plastic properties: Manufacturer datasheets; Modern Plastics Handbook (McGraw-Hill).
- Food contact safety: US FDA 21 CFR Part 177 (Indirect food contact substances).
- 3D printing materials: Manufacturer datasheets (PLA, ABS, PETG, nylon).
Disclaimer. Plastic selection depends on temperature, chemical exposure, mechanical load, UV exposure, and regulatory requirements (food contact, medical, electrical). Confirm with manufacturer datasheets for any critical application.