Key Physico-chemical Properties of Packaging Films and Their Impact on Food Safety

Not all packaging films are created equal. The thin layer of plastic wrapped around a piece of fresh meat or a block of cheese does far more than just hold the product together – its physical and chemical makeup determines whether the food inside stays safe, fresh, and appealing for days or weeks. These characteristics, collectively known as physico-chemical properties, are the engineering backbone of modern food packaging. Understanding them is essential for anyone involved in food production, packaging design, or quality assurance.

What are physico-chemical properties of packaging films? 🔗

Physico-chemical properties are the measurable physical and chemical characteristics of a material that govern how it performs under real-world conditions. According to research published in PMC, the quality and safety of food products greatly depend on the physico-chemical properties of the packaging material used. In practical terms, these properties tell us how strong a film is, how much it can stretch, whether it can be heat-sealed, how well it blocks gases, and how transparent it appears. Together, they determine whether a specific film is suitable for packaging fresh meat, dry snacks, cooked meals, or any other food category.

Key physico-chemical properties and what they mean 🔗

Tensile strength 🔗

Tensile strength measures how much pulling force a film can withstand before it tears or breaks. It is typically expressed in megapascals (MPa) or Newtons per unit area. Mechanical properties like tensile strength are crucial for food packaging because they determine whether a film can survive handling, transport, and storage without rupturing and exposing the contents to contamination. Films with high tensile strength are preferred for vacuum-packed meats and heavy products where physical stress on the packaging is considerable. Petroleum-based plastic films such as polyethylene, polyvinyl chloride, and polypropylene have been widely used due to their good mechanical properties, which include tensile strength, elongation at break, and resistance to deformation.

Elongation at break 🔗

Elongation at break (also called ultimate elongation) is the percentage increase in a film’s length before it snaps under tension. Ultimate elongation values of several hundred percent are common for elastomers and packaging polyolefins, while rigid plastics typically show values under 5%. A high elongation means the film is flexible and can accommodate stretching without cracking – a critical property for stretch wraps and vacuum packaging applications. Importantly, the combination of high tensile strength and high elongation results in a material with high toughness, which is ideal for packaging that must resist both pulling and puncturing forces.

Heat sealability 🔗

Heat sealability refers to a film’s ability to form a strong, airtight bond with itself or another film when exposed to heat and pressure. It is one of the most operationally critical properties in packaging because an unreliable seal compromises the entire protective function of the package. Once air has been replaced or eliminated from a package, sufficient seal integrity is required to maintain a low oxygen concentration inside – poor seals allow oxygen to re-enter and negate any barrier advantage the film provides. Key sealing parameters include the initiation temperature, optimal sealing temperature range, applied pressure, and dwell time. Critical sealing parameters include seal initiation temperature, optimal sealing temperature range, sealing pressure requirements, dwell time for adequate seal formation, hot tack strength during seal cooling, and final seal strength and integrity.

Gas transmission rate (GTR) 🔗

Gas Transmission Rate (GTR) – and more specifically, the Oxygen Transmission Rate (OTR) – measures how much gas passes through a film over a given time period. It is typically expressed in cc/m²/day. OTR is the steady-state rate at which oxygen gas permeates through a film at specified conditions of temperature and relative humidity. This matters enormously for food safety: oxygen drives the chemical and biological reactions responsible for rancidity, mold, microbial growth, and color change. Fresh meats and cheeses are often packed in vacuum-sealed or MAP environments with low OTR packaging to limit oxygen, keeping the product fresh for longer. A study published in the Journal of Food Protection confirmed that both packaging atmosphere and film OTR significantly affect the growth rate of spoilage bacteria on meat fillets, underscoring how directly this property impacts food safety outcomes.

Beyond oxygen, the Water Vapor Transmission Rate (WVTR) – sometimes called moisture vapor transmission rate (MVTR) – measures how much moisture passes through the film. For many foods, packaging design must balance oxygen and water transmission rates to optimize freshness and food safety. Dry products like snacks and spices need films with very low WVTR, while certain fresh produce benefits from controlled moisture exchange.

Clarity 🔗

Clarity, or optical transparency, refers to how clearly the product can be seen through the film. This is both a marketing and a food safety property. High clarity allows consumers to inspect the product visually without opening the package, making it easier to identify discoloration, leakage, or spoilage. PET films are characterised by outstanding clarity and gloss, making them popular for retail display packaging. In meat packaging specifically, visibility directly supports consumer confidence and purchasing decisions.

Common packaging film materials and their physico-chemical profiles 🔗

Polyethylene (PE) 🔗

Polyethylene is the most widely used polymer in food packaging, available in several forms – low-density (LDPE), linear low-density (LLDPE), and high-density (HDPE). LDPE film is a translucent, soft film with excellent chemical stability, heat sealability, water resistance and moisture resistance, and freezing resistance. LLDPE improves on this with higher tensile and impact strength while retaining good heat sealability, making it a preferred choice for heavy-duty food bags, frozen meat packaging, and stretch films. HDPE is stiffer, which suits applications requiring packages to maintain their shape. The primary limitation of polyethylene in high-barrier applications is its relatively high oxygen transmission rate, meaning it alone is insufficient for oxygen-sensitive products like fresh red meat.

Polypropylene (PP) 🔗

Polypropylene is a thermoplastic with high clarity, high gloss, and good tensile strength. It has a higher melting point than PE, making it suitable for applications requiring sterilization at elevated temperatures. Cast polypropylene (CPP) offers higher tear and impact resistance, better cold temperature performance, and better gas barrier and heat-sealing properties, whereas biaxially oriented polypropylene (BOPP) offers higher tensile strength, higher stiffness, lower elongation, and lower haze. CPP is widely used as the inner sealant layer in retort pouches and confectionery packaging, while BOPP is typically used as the printed outer layer in laminated structures. Like PE, standard PP has a moderate OTR and often requires lamination with barrier materials for oxygen-sensitive foods.

Nylon (polyamide) 🔗

Nylon, or polyamide (PA), stands apart from PE and PP primarily due to its exceptional gas barrier and mechanical performance. Nylon film is highly durable with good transparency, gloss, tensile strength, heat and cold resistance, oil resistance, and excellent oxygen barrier properties. These qualities make it a natural fit for packaging greasy foods, meat products, vacuum-packed foods, and steamed or retort products. However, nylon has poor barrier properties to water vapor, high moisture absorption and moisture permeability, and poor heat sealability. For this reason, nylon is almost always used in combination with other films – typically laminated with PE or LLDPE – to compensate for its sealing limitations while retaining its superior oxygen barrier and mechanical toughness.

How these properties determine film selection for food packaging 🔗

No single film material excels across all physico-chemical properties, which is why packaging materials now include laminates, developed by systematically integrating materials with different inherent properties to improve the functionality of the final material. A typical vacuum pack for fresh meat, for instance, might combine a nylon outer layer for strength and oxygen barrier performance with an LLDPE inner sealant layer that provides heat sealability and moisture resistance. Modified atmosphere packaging (MAP) for fresh red meat takes this further: barrier films designed to prevent the exchange of gases are mainly used with non-respiring products like meat and fish, with the film’s OTR engineered to hold a specific gas composition – typically a combination of CO₂ and oxygen or nitrogen – stable over the product’s shelf life.

Barrier properties including water vapor transmission rate, gas transmission rate, light, flavor, and aroma of multilayer packaging films are superior compared to those of monolayer packaging films, and this directly impacts the shelf life of packaged foods. When selecting a film, food producers and packaging engineers evaluate all of the key physico-chemical properties in concert – not in isolation. A film that blocks oxygen effectively but cannot form a reliable heat seal, for example, will fail in production. Similarly, a film with excellent tensile strength but high moisture transmission will underperform when packaging products sensitive to humidity.

Food safety implications of film properties 🔗

The connection between packaging film properties and food safety is direct and measurable. Films with low OTR slow the oxidation that produces off-flavors and rancidity. Heat-sealed films, when properly sealed, prevent the ingress of pathogens and contaminants. Films with adequate mechanical strength reduce the risk of physical damage and contamination during transit. Research on ground chicken leg meat showed that aerobic plate counts increased at a faster rate in packaging films with higher oxygen transmission rates, confirming that even among films used for the same product, OTR differences produce measurable differences in microbial safety.

There is also the matter of chemical migration – the potential for substances within the film to transfer into the food. Food packaging serves purposes of food product safety and easy handling, but the significance of transferring harmful materials from packaging materials into foods is of growing concern. Regulatory bodies including the U.S. Food and Drug Administration (FDA) and the European Food Safety Authority (EFSA) have established limits on the migration of chemical substances from packaging into food, and film physico-chemical composition plays a central role in whether a material meets those standards.

Ultimately, selecting the right packaging film is not a one-size-fits-all decision. It requires a thorough understanding of each physico-chemical property, the specific demands of the food product being packaged, and how different materials can be combined to meet both protective and regulatory requirements. As food supply chains grow longer and consumer expectations for freshness and safety increase, these material science fundamentals become more important – not less.

What do you think? Given that no single packaging film excels in all physico-chemical properties, how should food producers weigh the trade-off between barrier performance and heat sealability when designing packaging for fresh meat? And with rising concern over chemical migration from plastics into food, do you think biodegradable or bio-based films will eventually match conventional materials across all the key physico-chemical benchmarks?

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC10097132/
2. https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2022.1000116/full
3. https://www.matweb.com/reference/tensilestrength.aspx
4. https://www.polyprint.com/understanding-film-properties/flexographic-otr/
5. https://shkpack.com/blogs/news/common-packaging-films-used-in-food-industry-and-their-applications
6. https://blog.icpg.co/understanding-otr-mvtr-specifications-for-barrier-food-packaging
7. https://www.pennpac.com/blog/understanding-transmission-rates-in-food-packaging-film/
8. https://pubmed.ncbi.nlm.nih.gov/16629045/
9. https://www.market-prospects.com/articles/types-of-plastic-film
10. https://www.cloudflexfilm.com/the-structure-and-application-of-flexible-packaging-composite-bags/
11. https://www.firstagroup.com/resources/plastic-films.html
12. https://www.flexipack.com/en/exploring-the-different-types-of-plastic-film/
13. https://pmc.ncbi.nlm.nih.gov/articles/PMC8325021/
14. https://en.wikipedia.org/wiki/Modified_atmosphere
15. https://pmc.ncbi.nlm.nih.gov/articles/PMC7956554/
16. https://pubmed.ncbi.nlm.nih.gov/7479518/
17. https://www.fda.gov/
18. https://www.efsa.europa.eu/