Here’s a clear, practical comparison of polyethylene (PE) vs polypropylene (PP) for packaging — their properties, common forms, typical uses, pros/cons, recycling info, and guidance on which to choose.

Key materials and forms

• Polyethylene (PE)
  • Common types used in packaging: low-density PE (LDPE), linear low-density PE (LLDPE), high-density PE (HDPE).
  • Typical forms: films (bags, stretch/shrink film), squeeze bottles, liners, pouches, flexible packaging.
• Polypropylene (PP)
  • Typical forms: oriented polypropylene (OPP) film, cast polypropylene (CPP) film, injection-molded containers, rigid tubs, hot-fill or microwaveable trays.

Mechanical & thermal properties

• Strength & stiffness
  • PE: generally more flexible and less stiff (LDPE/LLDPE very flexible; HDPE stiffer).
  • PP: stiffer and stronger (higher tensile strength) than comparable PE grades.
• Impact resistance
  • PE (especially LDPE/LLDPE): excellent impact resistance and toughness at low temperatures.
  • PP: good impact resistance at room temperature, but becomes brittle at lower temperatures.
• Heat resistance & melting point
  • PE: melts roughly 105–135°C depending on grade (LDPE ~105–115°C; HDPE ~125–135°C).
  • PP: higher melting point, about 160–170°C — better for higher-temperature uses (hot-fill, sterile packaging, microwaveable containers).
• Sealability & heat-sealing window
  • PE: easy to heat-seal, broad sealing window (great for many flexible packages).
  • PP: narrower sealing window; CPP is used as a sealant layer because it seals easier than OPP.

Barrier properties (moisture, gas, aroma)

• Moisture (water vapor) barrier
  • PE: good moisture barrier — commonly used for moisture-sensitive products.
  • PP: similar to PE or slightly better depending on film orientation; both are poor oxygen barriers compared to some specialty films.
• Oxygen/CO2 barrier
  • Both PE and PP have relatively low oxygen-barrier properties compared with nylon, EVOH, or metallized films. For high oxygen-barrier needs, multilayer structures or metallization/EVOH are used.
• Aroma/chemical permeability
  • PP typically has slightly better resistance to permeation by some chemicals and aromas, but both are often combined with barrier layers when needed.

Optical properties

• PE films: generally less crystal clarity than PP (LDPE hazier; HDPE opaque).
• PP films (especially OPP): excellent clarity and gloss — commonly used for retail packaging where appearance matters.

Processing and formability

• PE: excellent flexibility, stretchability (LLDPE used for stretch film), good for extrusion, blow molding, film casting.
• PP: good dimensional stability, can be oriented (OPP) for higher stiffness and optical properties; used widely in thermoforming, injection molding and as film for printed labels.

Printability and finishing

• PP (OPP) films: accept high-quality printing and graphics well (preferred for attractive retail packaging).
• PE: printability is okay but typically requires treatment (corona, plasma) for best ink adhesion; less glossy.

Food contact & chemical resistance

• Both PE and PP are widely accepted for food contact packaging and are chemically inert for many foods.
• PP’s higher heat tolerance makes it preferable for hot-fill foods and microwaveable containers; PE is common for chilled/frozen foods and flexible wrap.

Environmental & recycling

• Recycling codes:
  • PE: HDPE is #2, LDPE is #4.
  • PP: polypropylene is #5.
• Recyclability: all are recyclable in principle, but actual recycling depends on local streams and contamination. PP recycling infrastructure has expanded but is still less available in some areas compared with HDPE.
• Weight & material efficiency: PP’s higher stiffness can allow thinner structures for the same strength (lighter packs possible), potentially reducing material use.
• End-of-life: both are plastic; compostable/biodegradable options differ and are separate technologies.

Cost

• Costs vary with market and grade, but generally PE (especially commodity LDPE and HDPE) is cost-competitive; PP can be similar or slightly more expensive depending on grade and processing requirements. Orientation (OPP) and specialty films add cost.

Typical applications (quick list)

• PE
  • Grocery bags, trash bags, flexible pouches, shrink/stretch film, liners, milk jugs (HDPE), squeeze bottles.
  • Frozen food bags, agricultural film, protective wrap.
• PP
  • Rigid containers/tubs (yogurt cups), thermoformed trays, bottle caps, microwaveable containers, OPP candy/snack wrappers, laminated pouches (CPP heat-seal layer).
  • High-clarity printed retail packaging, labels, tapes.

Pros & cons summary

• Polyethylene (PE)
  • Pros: flexible, excellent impact resistance, good moisture barrier, broad seal window, cheaper in many uses, good for cold or flexible packaging.
  • Cons: lower stiffness and clarity, lower heat tolerance.
• Polypropylene (PP)
  • Pros: higher stiffness & strength, better heat resistance, superior clarity (OPP), good for hot-fill and rigid containers, can enable thinner structures.
  • Cons: narrower sealing window, can be brittle at low temperatures, print/seal processing can be more demanding.

How to choose (practical guidance)

• Choose PE when:
  • You need flexible, stretchable film (stretch/shrink, LDPE/LLDPE).
  • Good low-temperature toughness or a broad heat-seal range is required.
  • Cost-sensitive, moisture barrier and simple food-contact film are priorities.
• Choose PP when:
  • You need higher stiffness, clarity, or higher temperature resistance (hot-fill, microwave-safe).
  • You want high-quality printed packaging (OPP) or rigid containers.
  • You want to reduce material gauge while maintaining strength.
• Consider multilayer structures:
  • Often the best solution is a multilayer film combining PE, PP, EVOH, nylon, or metallized layers to tailor barrier, sealability, printability, and strength.
• Consider recyclability and local collection:
  • Check local recycling streams — choosing a material that is accepted locally improves end-of-life outcomes.

If you’d like, I can:

• Recommend material/structure for a specific product (food type, shelf life, temperature, desired appearance).
• Suggest multilayer film constructions for given barrier and processing needs.
• Provide a short checklist for testing (seal strength, transit, shelf-life study).

Which would you like help with next?