Polypropylene is the lightest common resin and one of the lowest cost. Homopolymer is stiffer and handles more heat. Impact copolymer adds rubber so parts survive drops and cold. Both resist most acids, bases and solvents, and PP makes a living hinge that lasts.
Typical Polypropylene properties
| Property | Homopolymer | Impact copolymer | Test method |
|---|---|---|---|
| Density | 0.90–0.91 g/cm³ ~0.033 lb/in³ | 0.90–0.91 g/cm³ ~0.033 lb/in³ | ASTM D792 / ISO 1183 |
| Tensile strength | 31–37 MPa 4,500–5,400 psi | 20–28 MPa 2,900–4,100 psi | ASTM D638 / ISO 527 |
| Flexural modulus | 1.2–1.8 GPa 174,000–261,000 psi | 0.9–1.4 GPa 131,000–203,000 psi | ASTM D790 / ISO 178 |
| Notched Izod impact | 20–50 J/m 0.4–0.9 ft·lb/in | 60–500 J/m 1.1–9.4 ft·lb/in | ASTM D256 |
| Heat deflection, 1.8 MPa (264 psi) | 50–60°C 122–140°F | 45–55°C 113–131°F | ASTM D648 / ISO 75 |
| Water absorption, 24 h | 0.01–0.03% | 0.01–0.03% | ASTM D570 / ISO 62 |
| Mold shrinkage | 1.0–2.0% 0.010–0.020 in/in | 1.0–2.0% 0.010–0.020 in/in | ASTM D955 / ISO 294-4 |
Typical ranges for standard grades, dry as molded, from published data sheets. Your grade’s own data sheet and the lot COA are what count. Notched Izod uses 3.2 mm (1/8 in) bars.
Processing and drying
| Processing | Homopolymer | Impact copolymer |
|---|---|---|
| Melt temperature | 374–525°F / 190–274°C | 392–500°F / 200–260°C |
| Mold temperature | 50–203°F / 10–95°C | 59–149°F / 15–65°C |
| Drying | 167°F / 75°C, cosmetics only, 2 h when required | 167°F / 75°C, cosmetics only, 2 h when required |
| Target moisture | Up to 0.2% has no effect | Up to 0.2% has no effect |
| Max barrel residence | Purge if idle >30 min | Not published |
| General | Homopolymer | Impact copolymer |
|---|---|---|
| Clarity | Translucent | Translucent to opaque |
| Chemical resistance | Excellent: acids, bases, most solvents | Excellent: acids, bases, most solvents |
Starting points only. See the full processing temperature chart and drying guide for every resin.
What changes these numbers
- Melt flow range is huge. PP grades run from under 1 to over 100 g/10 min. Match the melt flow to the process and wall thickness before comparing anything else.
- Cold impact. Homopolymer gets brittle near freezing. Impact copolymer stays tough well below it.
- Fillers change everything. Talc and glass-filled PP are much stiffer and shrink less. Their numbers are not on this table.
- Shrinkage. PP shrinks a lot and varies with wall thickness and packing, so flat parts can warp.
Common Polypropylene grades
- Homopolymer
- Impact copolymer
- Random copolymer (clearer)
- Talc-filled, 10% to 40%
- Glass-filled
- UV-stabilized grades
- Clarified and nucleated grades
Common questions
What is the density of polypropylene?
About 0.90–0.91 g/cm³ (0.033 lb/in³). It floats in water.
What is the difference between PP homopolymer and copolymer?
Homopolymer is stiffer, stronger and a little more heat resistant. Impact copolymer has rubber mixed in for toughness, especially in the cold. See homopolymer vs. impact copolymer.
Does polypropylene need drying?
Usually not. Up to 0.2% moisture has no effect. Dry at about 75°C for 2 hours only for cosmetic parts or filled grades.
Need Polypropylene, or something close?
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province