Replacing plastic cushioning with heavier corrugated cardboard can increase the carbon footprint of transport packaging, particularly in global supply chains that rely on air freight, a study has found.
A life-cycle assessment found that a corrugated-cardboard cushioning system, which was 35% heavier than the heavier of two plastic-cushioned alternatives, had the highest carbon footprint. The lightest option, using expanded polypropylene (EPP) cushioning, had the lowest.
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The findings do not show that plastic is inherently lower-carbon than cardboard. Instead, they demonstrate how packaging weight can interact with transport distance and mode to influence the emissions associated with material substitution.
Published in Resources, Conservation and Recycling, the study assessed packaging used to distribute a 32kg information and communications technology (ICT) product to customers worldwide.
Why packaging weight matters
The researchers compared three single-use packaging systems.
One used EPP cushioning, another used expanded polyethylene (EPE), and the third replaced the plastic cushioning with corrugated cardboard. All three used corrugated-cardboard outer boxes, although their dimensions differed.
The packaging systems had passed the company’s standardised packaging tests and were assumed to provide comparable product protection.
The cardboard-cushioned system was 35% heavier than the heavier of the two plastic-cushioned systems. The additional weight increased transport-related emissions, with the effect becoming more significant over long distances and when shipments travelled by air.
The researchers concluded that alternatives to plastic should be developed “without increasing packaging weight”.
The significance of additional weight, however, depends on the supply chain in which the packaging is used.
Air freight magnifies the impact
Manufacturing was the largest contributor to the carbon footprint of all three packaging systems. Transport accounted for about 30% to 36% of the total carbon footprint.
Air freight had a disproportionate effect.
Although it accounted for only about 9% of shipments to customers, it was responsible for approximately 80% to 82% of the total transport impact.
The products travelled by road, sea and air, with air-freight distances ranging from 1,500km to 10,000km.
This made the transport footprint particularly sensitive to additional packaging weight.
The analysis found that transport had a much smaller effect over shorter supply chains, illustrating why the carbon implications of the same packaging design can change according to where and how a product is distributed.
How much lightweighting makes a difference?
When manufacturing, transport and end-of-life were assessed together, the corrugated-cardboard cushioning system had the highest carbon footprint.
The EPP system, which had the lowest packaging weight, had the lowest carbon footprint.
However, a sensitivity analysis showed that reducing the weight of the cardboard-cushioned system could substantially change the comparison.
The researchers calculated that reducing its weight by 12%, to 4.25kg, would bring its total carbon footprint down to approximately the same level as the EPE system.
To reach the carbon footprint of the lighter EPP system, the amount of corrugated cardboard used would need to be reduced by almost half.
The findings demonstrate why lightweighting can play an important role in packaging decarbonisation. Replacing one material with another may not reduce emissions if the new design requires substantially more material and adds weight to shipments.
Material choice still matters
Weight is not the only factor determining the environmental performance of packaging.
The researchers assessed four environmental indicators beyond climate change: terrestrial ecotoxicity, human toxicity, marine ecotoxicity and fossil depletion.
EPP had the lowest impact across all four categories. The cardboard-cushioned system ranked second in three of them.
The analysis also identified environmental impacts associated with plastics at different stages of their life cycle. Plastic production contributed to fossil-resource depletion, while plastic waste produced greater marine-ecotoxicity impacts at end-of-life in the study’s model.
The results show why plastic reduction and carbon reduction should not be treated as interchangeable measures of packaging sustainability. A system that performs better on greenhouse-gas emissions can produce different results across other environmental indicators.
End-of-life changes the calculation
Waste-management systems can also influence the carbon footprint of packaging.
Landfilled cardboard can generate methane as it decomposes in oxygen-free conditions, giving it a larger end-of-life carbon contribution than landfilled plastic cushioning in the study’s model.
Different treatment routes changed that calculation. Under the study’s model, recycling or incinerating cardboard avoided the methane emissions associated with landfill.
Under the study’s 100% recycling scenario, end-of-life accounted for less than 1% of the carbon footprint of all three packaging systems.
The researchers also noted uncertainty in waste-treatment data for some markets. Reliable information was unavailable in some regions, requiring broader waste statistics to be used for cardboard in parts of Asia and Latin America.
The findings highlight how regional recycling, incineration and landfill systems can influence the results of packaging life-cycle assessments.
No universal winner
The findings should not be interpreted as evidence that plastic packaging is generally better for the climate than cardboard.
The research covers one B2B supply chain, one 32kg ICT product and three specific packaging designs. Its results were strongly influenced by long-distance distribution and the use of air freight.
The transport analysis also focused on packaging weight and assumed that transport vehicles generally reached their weight limits before exhausting their available cargo volume.
Packaging dimensions can also affect transport efficiency. A lightweight package that occupies more space may affect how efficiently trucks, aircraft and shipping containers can be loaded.
The researchers therefore identified packaging volume, and its interaction with weight, transport distance and transport mode, as an area for further research.
Different products, packaging designs, logistics networks and waste-management systems could produce different results.
The study is therefore best understood not as a ranking of plastic against cardboard, but as evidence that the environmental performance of transport packaging depends on the wider system in which it is used.
Designing for lower emissions
For packaging designers and supply-chain managers, the study suggests that material substitution should be assessed alongside its logistics consequences.
A switch from plastic to fibre-based cushioning may support plastic-reduction targets but increase transport emissions if it results in a substantially heavier package, particularly in supply chains dependent on air freight.
Conversely, lightweight plastic cushioning can reduce transport-related emissions while creating different environmental impacts elsewhere in its life cycle.
Packaging decisions therefore need to account for the amount of material used, package weight and volume, manufacturing, transport distance and mode, and likely end-of-life treatment.
The study’s broader lesson is that packaging cannot be assessed separately from the supply chain it serves. Reducing plastic use and reducing carbon emissions can both be valid environmental objectives, but they will not always favour the same packaging design.
