Selecting the Right Packaging Material - What You Might Not Know

Clear packaging is a popular choice for many consumer-packaged goods (CPGs) because customers intuitively prefer to see the product prior to making a purchase. When developing clear packaging material for CPGs, brands typically consider four options given their clarity capabilities—glass, polyethylene terephthalate, polystyrene, or polypropylene.

• Glass has a long history as a go-to choice for transparent packaging and containers, given its clarity and perceived sustainability benefits. But as technology has developed, the gap between glass and other materials has diminished.
• Polyethylene Terephthalate (PET) is routinely considered for clarity and strength purposes, and while its recyclability is a strong differentiator, it lacks heat-resistant characteristics.
• Polystyrene (PS) is a type of plastic known for clarity, density, and stiffness capabilities—think of the satisfying snap of a four-pack yogurt packaging—that many believe are exclusive to this type of plastic.
• Polypropylene (PP) is a lightweight, highly heat-resistant plastic that can be enhanced for a range of applications.

Given each material’s inherent properties, it may seem that glass, PS, or PET is the right choice. Thanks to advances in additive solutions that enhance the material, PP is fast becoming a viable alternative. But when considering the full slate of packaging value points—performance properties, financial considerations, and environmental impact—the resulting winner may surprise you. 

Glass or Polypropylene?

Glass is often touted as a preferred packaging choice over plastic, and that perception comes down to two major characteristics: Glass is seen as more transparent and more sustainable. 

Especially in food packaging, clarity is an integral part of most packaging material decisions, and no one can deny that glass is an incredibly transparent material. However, new generations of clarifier solutions imbue PP with glass-like clarity.

With the industry’s heightened focus on sustainability, brands are eager to find and incorporate sustainable packaging solutions. While glass might seem like the better option, the reality is clarified PP may actually surpass glass in sustainable value chain benefits. The density of glass is, on average, three times that of PP. ^[1] Glass packaging is 12 to 14 times heavier than plastic packaging due to both the density disparities in materials and the necessity for thicker construction in glass containers to address material limitations and prevent breakage.

The weight of glass adds additional transportation costs and is typically more expensive to manufacture and finish into packaging. The increased weight also drives greenhouse gas (GHG) emissions, given the additional resources and energy needed to produce and transport glass. When comparing plastic soap containers to glass soap containers, plastic containers offered an estimated GHG savings of 15%, savings that impact the entire supply chain and further a host of emission reduction targets.

Polyethylene Terephthalate or Polypropylene?

If you’ve committed to the idea of using plastic for clear packaging, you may be considering polyethylene terephthalate (PET), polystyrene (PS), or polypropylene (PP), given their clarity ability.

PET provides a number of performance packaging characteristics in addition to clarity, namely strength, density, and end-of-use recyclability, especially as considered with PS. In many respects, PET and PP offer brands the same opportunities with one significant drawback: PET is not a heat-resistant material.

Ever noticed a food packaging lid’s disclaimer? Or the instructions on a package that state an item is not microwave-safe? Chances are, those pieces are PET, which is highly susceptible to heat and cannot be exposed to extreme temperatures without breaking down. PET is not appropriate for packaging exposed to high and variable temperatures, but using PET can often create risky situations where it might accidentally—or even purposefully—be exposed to heat. It’s safer to remove the risk altogether and protect the integrity of the packaging during transit, storage, and customer use.

Polystyrene or Polypropylene?

PS is a heavier polymer than PP, and in its natural state, PS is hard and clear—seemingly a better choice for packaging.

There end up being several pitfalls to PS when compared to PP. PS has a density of 1040 kg/m³, and the material is extremely brittle. The density contributes to a heavier end product, and with that weight comes an increased carbon footprint and greater environmental impacts. Packaging made with PS is also classified as non-recyclable under the Association of Plastic Recyclers’ definition and fails to meet the criteria for consumer access to collection established by the U.S. Federal Trade Commission’s Green Guides.

By contrast, and especially when treated with the latest additive solutions, PP becomes the ideal plastic for a variety of packaging. Enhanced with the right clarifier additive, the milkiness of PP transforms to clarity on par with, even exceeding, PS. It is a lightweight polymer with application-driven strength, achieved with specified processing variables tailored to use. PP packaging can also be reused and microwaved, adding to its usable life cycle until it can be recycled and repurposed in its end-life state.

Using PP lends additional value when considering inter-material replacement strategies (IMR). In past packaging iterations, PS may have been selected because of its high heat-deflection temperature. Using PP as an alternative in these applications specifically—think rib tray lids or chicken domes, where heat resistance is critical—means that the entire packaging can become mono-material and, therefore, even more recyclable.

The Clear Winner: Polypropylene

The entire value chain can realize financial, performance, and sustainability advantages by making PP their packaging material of choice.

• The entire value chain enjoys the versatility of PP as the lowest-density polymer suited to a variety of use cases.
• Brand owners can harness the low energy requirements and reduced carbon footprints achieved from the PP manufacturing process.
• Finally, end-of-life pathways for PP include high-energy recovery value and high recycling potential, contributing to the circular economy for plastics.

Ready to make the switch to PP packaging? Contact our team to discuss how Milliken’s additive solutions can enhance your PP selection.

[1] The density of glass is 2,450 kg/m³.

Ashby, Mike. Material Property Data for Engineering Materials. 5th ed., Department of Engineering, University of Cambridge, 2021. p. 8.