An In-Depth Guide to Polypropylene — PP's Moisture-Resistant Properties in Packaging

An In-Depth Guide to Polypropylene — PP's Moisture-Resistant Properties in Packaging

Tommy Lai |

Polypropylene (PP) reigns supreme for its versatility and reliability. As one of the most commonly used thermoplastics worldwide, PP is known for its moisture resistance and wide-ranging applications. 

Since its first polymerization in 1951, it has become essential in product packaging, be it food, machinery parts, and textiles. With global demand soaring to approximately 45 metric tons annually, PP serves domestic and industrial industries.

But beyond that, what's more about polypropylene? Why PP is an attractive material in various Vancouver packaging solutions? Let's explore more about PP's moisture-resistant properties and its role in modern and custom packaging.

Polypropylene: History and Composition 

Looking Back  

Polypropylene’s discovery dates back to the mid-20th century. It was first polymerized in 1951 by two researchers, J. Paul Hogan and Robert L. Banks. But, Italian scientists Karl Ziegler and Giulio Natta discovered the process, leading them to publish their findings. 

These contributions were recognized with the Nobel Prize in Chemistry in 1963. Since its inception, polypropylene has experienced exponential growth. It emerged as one of the most extensively utilized plastics across diverse industries. 

Its remarkable properties, cost-effectiveness, and ease of manufacturing have contributed to its widespread adoption. Today, polypropylene remains integral to numerous applications, highlighting its significance in materials and plastics.

Composition of Polypropylene: 

Definitions of Complex Terms: 


Atoms/small molecules that join together to create more complex structures like polymers.


A polymer made from two or more different types of monomers


A polymer made from a single type of monomer.

Chain-growth polymerization

A polymerization process where monomer molecules add to a growing polymer chain one at a time.

Propylene monomers polymerize

The process by which propylene molecules chemically bond together to form a polymer

Polypropylene polymer structure

The molecular structure of polypropylene consists of a repeating sequence of propylene units arranged in a long chain.

Hydrocarbon resin

A type of resin derived from the polymerization or copolymerization of hydrocarbon monomers

Polypropylene (or PP for short) is a thermoplastic polymer made up of propylene (or propene) monomer units. It is synthesized via chain-growth polymerization—a process in which propylene monomers polymerize to create the polypropylene polymer structure. 

This linear hydrocarbon resin is esteemed for its toughness, rigidity, and crystalline properties. Polypropylene can be manufactured as a homopolymer consisting of propylene units (or as a copolymer combined with other monomers), which offers versatility in its characteristics and performance.

Ways to Process PP for Packaging Materials

  • Injection Moulding: Molten PP is injected into a mould cavity to produce items like automotive parts, toys, and custom packaging with intricate shapes
  • Extrusion: PP is melted and forced through a die to create continuous shapes like pipes, tubes, and sheets.
  • Thermoforming: Heating a PP sheet makes it pliable enough to mould into specific shapes, commonly used for food containers, trays, and blister packs.
  • Blow Moulding: Air is blown into a molten PP parison (a tube-like structure) to form hollow objects such as bottles and containers. 
  • Film Extrusion: Molten PP is extruded through a narrow die to produce thin films used in packaging needs like bags, wrappers, and labels

Types of PP for Packaging Solutions

Polypropylene Homopolymer

The PP Homopolymer is the most commonly used grade for general purposes. It consists solely of propylene monomers and is found in a semi-crystalline solid state. It's an ideal material for packaging solutions due to its:

  • High stiffness
  • Good chemical resistance
  • Excellent temperature resistance

Polypropylene, Impact Copolymer

Impact copolymer polypropylene is a specialized copolymer containing a higher proportion of ethylene, enhancing its impact strength (especially in low temperatures). This makes it suitable for applications requiring high-impact resistance, such as brand packaging.

Polypropylene, High Melt Strength (HMS)

PP HMS is a material with long-chain branching with high melt strength and extensibility when molten. Key characteristics of PP HMS packaging include:

  • A wide range of mechanical properties
  • Excellent heat stability
  • Strong resistance to chemicals

This is extensively utilized for creating soft, low-density foams used in food packaging solutions. It's also employed in the automotive and construction sectors.

Other Types of Polypropylene

Polypropylene Copolymer

This type of PP is made by combining propene and ethene through polymerization. It includes:

  • PP Random Copolymer: Blends ethene and propene during production, usually with ethene units comprising up to 6% by mass. These units are randomly integrated into the polypropylene chains, resulting in flexible and clear materials.
  • PP Block Copolymer: The ethene content is higher, ranging from 5 to 15%. Co-monomer units are arranged in regular patterns or blocks. polymers are well-suited for demanding applications requiring high strength, such as industrial uses.

Expanded Polypropylene (EPP)

EPP is a closed-cell bead foam with very low density, used to make three-dimensional foam products. EPP bead foam features:

  • High strength-to-weight ratio
  • Excellent impact resistance
  • Good thermal insulation
  • Resistance to chemicals and water

Polypropylene Terpolymer

PP Terpolymer is made of propylene with ethylene and butane monomers randomly distributed in the polymer chain. It offers better transparency and is ideal for sealing film applications.

Bio-based Polypropylene

This is a bio-based version of PP, with its propylene monomer sourced from renewable feedstocks. The bio-based content can range from 30% to 100%.

Comparing Main PP Types 



PP Homopolymer

PP Copolymer

Impact Copolymer


0.895-0.92 g/cm³




HDT A(1.8 MPa)




Shore Hardness

65-76 D

75-80 D

65-75 D

Notched Impact Strength ASTM D256

10-50 J/m

5-30 J/m

50-120 J/m

Elongation at Break




Stress at Yield

20-50 MPa

30-50 MPa

20-40 MPa

PP: The Right Packaging for Business Brands

Here's why PP is the ideal packaging in Canada:

Flexible Packaging

Polypropylene is a top material for film extrusion, favoured over cellophane, metals, and paper due to its superior puncture resistance, low sealing threshold, and competitive price. PP Film is available as Cast Film or bi-axially oriented PP (BOPP). The film market is divided into three main sectors:

  • Food and Confectioneries: The largest sector, used for packaging items like candies, chips, and biscuits.
  • Tobacco: The second-largest sector, used for packaging tobacco products.
  • Clothing: Also a significant market for PP films.

Rigid Packaging

If you want to transport or store items, reusable and collapsible/stackable crates made from PP are excellent - ideal for Just-in-Time (JIT) solutions. Supermarket brands and the automotive supply chain are increasingly using them.

  • PP caps and closures have grown popular with the rise of PET bottles, especially for mineral water and edible oil.
  • Used in blow moulding to make bottles for condiments, detergents, and toiletries.
  • Used for thin-walled containers like yogurt pots, competing with PS and cardboard.  

PP and Its Moisture-Resistant Property 

Polypropylene is highly moisture-resistant, making it an excellent choice for BC customers looking to enhance their packaging services. This resistance stems from its non-polar, hydrophobic molecular structure, which prevents water molecules from penetrating or affecting the material.

The advantages of Polypropylene moisture resistance in packaging include:

  1. Preservation of Product Quality: Preserve the freshness and quality of products, especially food items, which can spoil or degrade when exposed to humidity.
  2. Extended Shelf Life: Extends the lifespan of company products by preventing mould growth, spoilage, and other moisture-related issues.
  3. Protection from External Elements: Shields company products from external moisture and humidity, ensuring they remain dry and intact during storage and transportation.
  4. Versatility: Suitable for a wide range of packaging services in Canada, including food containers, pharmaceutical packaging, and moisture-sensitive electronics.

Other Notable Properties of Polypropylene 

Refractive Index 

Approximately 1.49

Softening Temperature

Around 130°C

Melting Point


Poisson's Ratio


UL94 Fire Rating 

V-2, HB, V-0

Tensile Modulus

1.5-2.5 GPa

Coefficient of Linear Thermal Expansion x 10-5


Transparency (Visible Light Transmission)


Volume Resistivity x 1015


Arc Resistance

135-180 sec



Top PP Packaging Solutions in British Columbia, Canada


Product Name




16oz White PP Bowls (Base Only)

1000 pcs



115mm PP Plastic Lid for PB12-32 Paper Bowl

500 pcs



26oz PP Clear Hard Cup

500 pcs



48oz Microwaveable PP Black Square Container W/ Lid

150 sets



3 Compartment Square Clamshell PP Hinged Container 9x9x3″

150 pcs


Sealing Film 

PP Sealing Film for Cups 





Get PP from Reliable Packaging Company in British Columbia

Now you know the advantages of polypropylene as a packaging material, it's time to operate your business on a higher level by using quality packaging to package each product for improved brand reputation and customer satisfaction.

Do not let your effort go to waste. Serve your customers right with premium packaging solutions from a reliable BC packaging company. Order take-out supplies in bulk at Patek Packaging for durable and cost-effective products. Contact our customer service team now if you have questions regarding our premium products. 

Frequently Asked Questions 

Is polypropylene food safe?

Yes, PP is used for food containers and packaging because it is considered food-safe. PP is certified as food-safe and meets all relevant regulatory standards.

How long does PP last?

The lifespan of PP depends on factors like environmental conditions, UV radiation, chemical exposure, and mechanical stress. Under normal conditions and proper use, polypropylene can last for many years. It resists moisture, chemicals, and most environmental factors, maintaining its integrity over time. 

Is PP recyclable?

Yes, Polypropylene can be recycled and used to manufacture new products. Recycling PP contributes to waste reduction and resource conservation.