Switch from PS to PP with Milliken clarifiers for improved packaging performance

A growing number of companies are facing a critical challenge: How to transition to materials that support circular economic goals. PS, long used for its clarity and stiffness, is now seen as problematic because it’s classified as non-recyclable and often has a negative consumer perception. Its brittleness and higher density contribute to heavier packaging, which translates to higher emissions during transport and increased breakage.

On the other hand, PP better aligns with recycling goals. It’s widely recyclable, especially when used in mono-material solutions, and its lightweight nature reduces transportation emissions and energy use. As sustainability targets tighten, PP’s compatibility with these goals makes it a better choice for forward-thinking brands.
 

Customers naturally prefer clear packaging because they can see the product inside, which helps build trust and satisfaction. When it comes to choosing clear packaging, many companies have traditionally preferred looked polystyrene (PS). PS is known for its clarity and stiffness—think of the crisp snap of a yogurt pack. However, it comes with several downsides—the primary being that it is classified as non-recyclable in addition to being heavier and more brittle than PP. PS packaging also has a higher carbon footprint due to its density and fragility, leading to more breakage and waste.

With brands increasingly focused on advancing plastic circularity, companies are switching from non-recyclable materials such as PS. There are three main alternatives for transparent packaging materials: glass, polyethylene terephthalate (PET), and polypropylene (PP) with pros and cons associated with each.

Glass has long been a top choice for clear packaging. Its transparency and consumer-perceived sustainability make it popular, especially in food and beverage applications. However, glass is heavy—on average, three times denser than PP—which means it requires more material and energy to produce and ship. This added weight also results in higher transportation costs and greenhouse gas emissions. For example, switching from glass to plastic for soap containers can cut emissions by about 15%, benefiting the whole supply chain.

PET is another common choice due to its clarity, strength, and recycling compatibility. However, PET falls short in one key area: Heat resistance. You might notice that PET containers are often labeled ‘not microwave-safe’. This is because PET can break down when exposed to high heat, making it risky for certain applications like hot food packaging or microwaveable items.

This is where PP, enhanced with Milliken’s clarifier technology, steps in PP can now resemble the transparency of PS and even glass while being lighter, more durable, and improving recycling compatibility. With Millad® clarifier technology, PP’s natural milkiness is transformed into a clear, glass-like appearance, making it a strong contender for transparent packaging needs.

PP is also heat-resistant, so it can handle hot-fill applications, microwaves, and variable temperatures—situations where PET and PS fall short. In the past, PS was chosen for packaging like rib tray lids and chicken domes because of its heat resistance. Now, PP enhanced with Millad® clarifiers can take on these roles while offering a mono-material solution more compatible with recycling infrastructures.

With its balance of clarity, durability, recycling compatibility, and reduced breakage and waste, PP is quickly becoming the preferred choice for clear packaging.

 

PP offers a balanced blend of properties that address modern packaging needs:

 

Moreover, PP’s density advantage (lower than PS or glass) means less material is required, translating to transportation cost and energy savings. Its heat resistance makes it suitable for food packaging and appliances—sectors that are increasingly adopting PP to meet consumer demands for reusable, durable, and recycling compatible materials.
 

For a long time, transparent packaging was mostly made from glass, PS, and PET because of their clarity and premium look. Milliken’s materials science innovations have enhanced the transparency of PP, overcoming the haze issues. Millad® clarifiers give PP a glass-like clarity, rivaling the transparency of traditional materials while providing sustainability benefits and cost advantages.

 

HIPS to PP in probiotic drinks

In food packaging, a major shift is happening as brands move from high-impact polystyrene (HIPS) to PP for products like probiotic drinks. Previously, HIPS was used for its rigidity and clarity in drink containers. However, PP now offers a similar visual appeal with the added benefits of improved recycling compatibility. 

Not only does switching from PS to PP improve recycling compatibility, but brands can now design mono-material packaging (bottle, cap, label—all in PP), further enhancing the packaging’s recycling compatibility. PS is not suitable for all package components, including the bottle, cap, and label of a probiotic drink. By contrast, PP can be used to make all of these components, resulting in a mono-material package, which is more recycling compatible and aligns with many brands' sustainability efforts to help advance plastic circularity. 

PS to PP in appliance components

Appliance manufacturers are also moving from PS to PP for components like refrigerator inner parts. Once made from brittle PS, these components are now being designed with PP for improved durability, resistance to cracking, and recycling compatibility. PP’s lightweight nature helps reduce product weight and shipping emissions, while its strength helps ensure bins stay intact during use and transport.

 

PS to PP in consumer-packaged goods

In the consumer-packaged goods (CPG) sector, brands are switching from PS to PP for applications like caps and closures. PS was once chosen for its stiffness, but it’s non-recyclable and susceptibility to cracking are making brands reconsider using the material. PP enhanced with Millad® clarifiers, now provides the clarity and strength needed for consumer packaging, while improving the recycling compatibility of the caps and closures.

This selection often encourages brands to revisit package designs to leverage mono-material PP solutions—where the entire package, including the cap and container, is made from PP—for heightened recycling compatibility.

A practical example of how PP and Milliken’s Millad® clarifier technology work together comes from Plastmore, a packaging company that partnered with a major Turkish chocolate brand.

The brand had been using crystal-clear PS packaging for its chocolates, but it wanted to improve sustainability benefits and reduce breakage during shipping. Replacing PS with PP wasn’t easy because the packaging needed to maintain its clear, premium look—a signature feature that customers recognized and loved.

Plastmore, with help from Milliken, developed a new packaging solution. They fine-tuned a PP formulation that could match the clarity of the original PS package while offering better sustainability performance.

• Reduced plastic usage: By switching to PP with Millad® clarifiers, the packaging design cut plastic use by 42%, providing a lighter-weight packaging solution.
• Lower carbon footprint: PP’s lower density and reduced energy requirements led to the manufacturing and transportation carbon footprint dropping significantly.
• Improved durability: PP’s higher resistance to breakage led to 7% fewer product losses during transit.
• Recycling compatibility: The new PP packaging was more compatible with recycling, advancing the brand’s sustainability goals.
• Cost-efficiency: PP also simplified labeling with in-mold labeling (IML), eliminating material complexity and reducing production steps.

The brand launched its new PP chocolate boxes in the Spring 2024 , and the switch was a success. Customers were happy with the familiar look, and the brand advanced its sustainability goals without sacrificing quality or appeal.
 

• Transparent, aesthetically pleasing packaging
• Recycling compatible and lighter weight, which saves shipping costs
• Heat-resistant enabling microwave-safe products Lower energy use during production

Why are more brands choosing PP over PS?

As companies across industries, especially in food packaging and appliances—seek ways to align with consumer expectations and company sustainability commitments, PP’s advantages over PS become clear:
 

• Recycling compatibility: PP is more compatible with existing recycling systems, unlike PS, which is often excluded from curbside collection.
• Transportation savings: Lower weight and energy use result in lower transportation costs and emissions.
• Functionality: PP withstands heat, allowing for microwave use. Increased durability allows for the product to be reused, extending the product's lifecycle.
• Cost-effectiveness: Despite initial tooling costs, the in-use cost of PP packaging can be lower due to its durability, reduced material requirements, and streamlined processing.

Forty-five years > Twenty-two markets

When Milliken scientists introduced the first PP clarifying technology, Millad®, nearly 45 years ago, they unlocked new opportunities for the plastics industry.

In the 1980s, PP’s hazy appearance limited its applications; consumers preferred materials with a clear, glass-like look. Millad® clarifiers addressed this challenge, enabling transparent PP, which began the use of PP in applications like packaging, food storage, and houseware. Over the years, as consumer demands shifted and technologies like LED lighting and e-commerce emerged, Milliken adapted its clarifiers to maintain PP’s fresh appearance on shelves and durability in transit.

Today, Millad® clarifiers help enable PP use across 22 markets, providing products with recycling compatibility, transparency, and production efficiency, all in an effort to advance plastic circularity.
 

The shift from PS to PP isn’t just a trend—it’s a strategic choice that supports better performance, lower costs, and enhanced sustainability benefits. Innovations like Milliken’s Millad® clarifier technologies are elevating PP’s aesthetic appeal, while its functional advantages and recycling compatibility make it a responsible choice for the future. In a world where consumers and regulators demand more from packaging materials, PP offers a pathway to advancing circularity.

DISCLAIMER: All figures and tables used in this article are copyright of Milliken.