PP (Polypropylene)
A light, cheap, chemically resistant plastic
Typical values for the temper in the title
Polypropylene is among the lightest plastics (about 0.91 g/cm³), cheap, highly resistant to acids, alkalis and many solvents, and stiffer than polyethylene. It has excellent flex-fatigue resistance, so it can make "living hinges", as in bottle caps.
It is used for containers and packaging, automotive parts (bumpers, interior parts), chemical piping and tanks, sterilizable lab equipment and fibers. Weaknesses: brittle when cold, and low UV resistance.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | 30–40 MPa | |
| Elongation A | 100–600% | |
| Modulus of elasticity E | 1.5–2.0 GPa | |
| Density ρ | 0.91 g/cm³ | |
| Max continuous service temperature | 100°C | |
| Heat deflection temperature (HDT) | 105°C | |
| Machinability | 75% | relative rating in the site database |
Structure and family
| Feature | Value | Meaning |
|---|---|---|
| Type | semi-crystalline polyolefin | chemical resistance and lightness |
| Tm melting | about 165 °C | |
| Density | about 0.91 | among the lightest plastics |
Typical values per producer data sheets.
Grades and versions
In engineering polymers, the choice is between an unfilled grade, filled grades (glass or carbon fiber) and special grades (bearing, medical, food). Filler strongly changes strength, stiffness and expansion.
| Version | Properties | When to choose it |
|---|---|---|
| Homopolymer | stiffer | parts and containers |
| Copolymer | more impact resistant, also when cold | bumpers, containers |
| Talc or glass filled | stiff and stable | automotive parts |
Applications
- Containers and packaging
- Automotive parts
- Chemical piping and tanks
- Sterilizable lab equipment
- Living hinges
Fabrication
Welding
Welds well by hot gas and butt fusion, so it is common in chemical tanks and piping.
Bonding
Very difficult without surface treatment.
UV
Not sun resistant without stabilizers.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| HDPE / LDPE | 20–30 MPa | Hot Gas / Butt Fusion | HDPE: more flexible, better in cold · material page |
| PVDF | 50 MPa | Hot Gas / Ultrasonic | PVDF: more chemical and heat resistant, expensive · material page |
| ABS | 45 MPa | Ultrasonic | ABS: tough, easy to bond · material page |
Common mistakes
Using homopolymer in cold with impacts
It breaks. For cold, copolymer.
Trying to bond with ordinary adhesive
It does not stick.
Leaving it exposed to sunlight
Embrittles without UV stabilizers.
Equivalents, standards and supply
| ISO | PP |
|---|---|
| ASTM | D4101 |
| Standards | ASTM D4101 |
| Forms | plate · rod · pellets · pipe |
| Producers | LyondellBasell · Borealis · SABIC |
Learn more
Values are typical for an unfilled grade (unless stated otherwise) and for comparison only. In polymers, properties depend on grade, filler, temperature, moisture and load duration. For design, rely on the producer data sheet for the specific grade. Sources: ASTM classification standards (D8033, D5205, D5204, D6394, D4067 and others), producer data sheets, and the METAL HUB materials database.
Updated: October 31, 2026