Plastics and Polymer Properties Reference
Look up density, tensile strength, elongation, service temperature, and uses for 18 plastics and polymers.
Calculate part weight from volume.
Selecting the right plastic for an application requires balancing multiple competing properties: strength, stiffness, temperature resistance, chemical resistance, processability, and cost. No single plastic is best at everything.
Key Properties for Plastic Selection:
Density (g/cm³): Directly drives part weight and material cost. PP at 0.90 g/cm³ provides more volume per kilogram than PVC at 1.40 g/cm³ — a 35% cost advantage per liter of finished part, all else equal. For injection molders, lower density means more shots per kilogram of resin.
Tensile Strength (MPa): The force per area the material can withstand before breaking. PEEK (100 MPa) and Nylon 66 (82 MPa) are high-performance structural options. LDPE (12 MPa) is suitable only for flexible, non-structural applications.
Elongation at Break (%): How much the material stretches before fracturing. High elongation (HDPE 800%, PP 400%) means ductile, tough materials that bend and stretch before failing. Low elongation (Epoxy 2%, PS 3%) means brittle materials that crack suddenly without warning.
Service Temperature (°C): The maximum continuous use temperature before the material softens, deforms, or degrades. PTFE (260°C) and PEEK (250°C) are exceptional; LDPE (80°C) fails in a hot car.
Thermoset vs Thermoplastic:
- Thermoplastics (HDPE, PP, PC, ABS, Nylon, etc.) can be melted and reprocessed. They are generally recyclable. They soften when heated.
- Thermosets (Epoxy, silicone RTV, polyurethane foam) undergo irreversible chemical crosslinking during cure. They cannot be remelted. They offer superior heat and chemical resistance.
Resin Identification Codes (RIC):
| Code | Resin | Common Use |
|---|---|---|
| 1 | PET | Beverage bottles |
| 2 | HDPE | Milk jugs, pipes |
| 3 | PVC | Window profiles, pipes |
| 4 | LDPE | Plastic bags, wrap |
| 5 | PP | Yogurt containers, living hinges |
| 6 | PS | Foam cups, CD cases |
| 7 | Other | Polycarbonate, PEEK, mixed |
Material Selection Example — Outdoor Electronics Enclosure: Options: ABS vs Polycarbonate (PC)
- ABS: cheaper, easier to machine/paint, good impact resistance indoors
- PC: superior impact resistance (nearly unbreakable), better UV stability outdoors, higher service temperature
- Winner for outdoor use: PC — despite higher cost, it resists UV yellowing and cracking that would ruin ABS after 2–3 years of sun exposure.
Part Weight Calculation: Weight (g) = Volume (cm³) × Density (g/cm³) This is the first calculation any injection mold designer performs to estimate material cost per shot.
Chemical Resistance Note: HDPE and PP resist most acids and bases. PVC resists many solvents. PTFE is nearly universally chemically inert. ABS is attacked by acetone (nail polish remover) and many organic solvents — a fact useful for welding ABS 3D prints with acetone vapor.