Quick, simple and clear way to distinguish between PP and PE

PE (polyethylene) and PP (polypropylene) are two of the most commonly used general-purpose plastics. The core differences are: PP is harder, more heat-resistant, and microwave-safe; PE is softer, more cold-resistant, and cheaper. The following is a detailed comparison from multiple perspectives:

I. Basic Definitions and Chemical Structures

PE (Polyethylene): Polymerized from ethylene monomers, its molecular chains have no side groups, resulting in a simple structure.

PP (Polypropylene): Polymerized from propylene monomers, its molecular chains have methyl side chains, resulting in a more complex structure.

II. Core Performance Comparison

Performance PE (Polyethylene) PP (Polypropylene)

Density 0.91–0.96 g/cm³ (Heavier than PP) 0.90–0.91 g/cm³ (Lightest of plastics)

Melting Point 105–135℃ 160–170℃ (Much higher)

Heat Resistance Poor, long-term ≤80℃, easily softens above 80℃ Good, long-term 100–120℃, microwaveable

Low Temperature Resistance Excellent, still tough at -60℃, not easy to crack Poor, becomes brittle around -20℃, easily breaks

Hardness / Rigidity Soft, good flexibility, strong impact resistance Hard, high rigidity, good bending resistance (unbreakable)

Transparency Mostly opaque or translucent Translucent, slightly better light transmittance than PE

Surface Feel Waxy, slippery Smooth, slightly glossy

Chemical Resistance Resistant to most acids and alkalis, but easily swells in non-polar solvents Stronger resistance to acids, alkalis, and organic solvents
Shrinkage: 1.5%–4% (relatively high) 1.0%–2.5% (relatively high)
Odor: Paraffin smell Petroleum smell
Recycling Symbols: 2 (HDPE), 4 (LDPE), 5
III. Common Types and Typical Applications
PE (Polyethylene)
LDPE (Low Density): Softest and most transparent, used for cling film, plastic bags, and hoses.
HDPE (High Density): Harder and stronger, used for milk bottles, medicine bottles, trash cans, and water pipes.
LLDPE (Linear Low Density): Good toughness, used for stretch film and heavy-duty packaging bags.
PP (Polypropylene)
Homopolymer PP: Best rigidity and heat resistance, used for microwaveable food containers, water cups, and bottle caps.
Copolymer PP: Better toughness, used for car bumpers, appliance casings, and toys.
Transparent PP: High transparency, used for transparent food containers and disposable syringes.

IV. Quick Identification Method
Check the symbol: The triangular recycling symbol at the bottom indicates PE (2/4) or PP (5). Touch test: PP is stiff and smooth; PE is soft and waxy.

Bending test: PP easily leaves white marks and breaks easily; PE is not easily broken even after repeated bending and leaves no obvious white marks.

Burning test: PE flame is yellow at the top and blue at the bottom, drips wax, and smells like paraffin; PP flame is yellow at the top and blue at the bottom, melts and drips, and smells like petroleum.