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Case study

What has the lowest impact: glass vs. plastic packaging

Plastic has a reputation issue. Sustainability-minded consumers look for products that ditch or minimize plastic packaging. Glass, paper, and other “organic“ solutions are gaining popularity. Is this justified? Is glass better than plastic?

Food & Beverage

Material choices largely determine the sustainability of our packaging products. This case study investigates whether glass packaging is more environmentally friendly than plastic packaging. It also explains how to assess and compare their sustainability!

For this, we will analyze two common retail products: a bottle of apple juice, and a jar of strawberry jam. What will the environmental impact be? And what happens when you take a full life cycle perspective? These questions are answered below.

Case 1: The Bottle Comparison.

Apple Juice Packaging - plastic bottle

In this case, we calculated the difference in impact between a plastic and a glass bottle packaging for apple juice. This analysis focused on the global warming potential of the product. So, how do the bottles compare?

Material Comparison

The apple juice bottling materials are:

  1. PET bottle
  2. PET bottle with 75% recycled PET content
  3. White glass bottle

The impact of the molding process, which shapes the raw material into its bottle form, is factored into the material impacts. We excluded the bottle caps from the analysis, assuming they would be the same for the three options.

For the end-of-life scenario (waste processing), we assumed the incineration of the plastic bottles and the recycling of the glass bottles.

Winner: White glass bottle!

Figure 1: Per kg material, glass has a lower global warming potential than plastic packaging. (Values are not shown in all images due to confidentiality).

Figure 1 shows the global warming impact of the material and bottle production (blue) vs. the impact of the waste processing (green). It looks like the environmental impact of the glass is lower! So should we prefer glass bottles next time in the supermarket?

Well… no!

While the global warming impact per kg of material is lower for the glass packaging, the weight of the glass makes a big difference.

Bottle Comparison

Glass bottles are much thicker and heavier than plastic bottles. Generally, the weight of glass packaging is multiple times heavier than plastic packaging! In our example, the 1 L glass bottle [1] is 17-18 times heavier than the plastic bottle [2].

When we ask ourselves whether to buy a glass or a plastic bottle, we should think about the impacts per bottle and not the impacts per kg material!

Figure 2 shows what happens when you increase the weight of the glass packaging material by a factor of 18.

Figure 2: Global warming impacts of the bottles.

Winner: Plastic bottle!

Because we need 17-18 times more material (in kg) for the glass bottle, its environmental impacts per bottle far exceed those of a plastic bottle!

Although waste processing has a lower environmental impact for glass bottles, the high material impacts cause a higher global warming potential for glass bottles compared to plastic bottles throughout their entire life cycle.

The heavier weight of the glass bottle means that in each transportation step along the supply chain, transporting the glass bottle costs more fuel. This makes shipping more expensive [3] and causes higher climate impacts.

While the depicted comparison is for CO₂ impacts, the environmental cost indicator (which contains more than just CO₂ impact), shows an even bigger difference: Here, the recycled PET bottle has almost 90% lower impacts than the glass bottle.

In summary, to be climate-friendly we should choose plastic bottles over glass, even if we don’t put them into the recycling bin!

How do we measure impact?

Before we jump into the second case, let’s quickly explain how we measure environmental impact.

Environmental impact is measured in a variety of impact categories. A commonly used one is Global Warming Potential, which is expressed in kg-CO₂-equivalent.

However, Global Warming Potential does not account for plastic waste or the toxicity impacts of the bottles. For the next analysis, we will follow the Environmental Cost Indicator (ECI), a Dutch environmental indicator that combines all environmental indicators into one monetary value (Figure 3). This monetary value accounts for CO₂, toxicity, and many other environmental impacts.

The analysis is based on a Life Cycle Assessment, the standard calculation method for environmental impacts across the life cycle of a product or service.

Scheme of ECI calculation method. Glass vs Plastic

Figure 3: Scheme of ECI calculation method

One of the core issues of measuring the environmental impact of packaging materials is that they are rarely a standalone product. If we took the environmental impact of the product itself into account, the packaging would drive a relatively small amount of the total impact. However, for this analysis, we compared only the packaging itself.

Case 2: The Jar Comparison

Here, we looked at three different packagings for strawberry jam:

  1. PET jar
  2. PET jar with 75% recycled PET content
  3. White glass jar

The glass jar is 7 times heavier than the plastic jar.

For the waste scenario for the plastic bottles, we assumed 50% incineration and 50% recycling. For glass, we assumed that 85% of the glass is recycled at the end of its life, and the remainder is sent to the landfill.

To make it more realistic, we also added the same lid, made from polypropylene, to all jars.

An overall advantage of plastic over glass is that fewer products with plastic packaging fail at the supermarket. We took this into account in the following full-lifecycle calculation!

Taking a full life cycle perspective and considering ALL environmental impacts, plastic packaging still scores better than glass!

Glass vs Plastics. Glass jar vs PET jar vs PET recycled jar

Figure 4: The three jars’ weighted score for all the environmental impacts (environmental cost indicator).

But what about plastic waste?

This analysis incorporates end-of-life scenarios – which means that the recycling or re-using of the materials was taken into account. The recycling rates are based on current Dutch waste statistics.

Plastic is overall more environmentally friendly in our examples. This was the case even when glass bottles were recycled and plastic bottles burned (assuming a less favorable waste processing for plastic in the bottle comparison).

Winner: Plastic packaging!

The analysis shows that the overall environmental impact of PET as a packaging material is lower. The main reason is that while plastic has a higher impact than glass per kg, we need much less kg of plastic to package our products.

Glass has an advantage in recyclability, however, because of the enormous difference in weight, the material and transport impacts of glass are significantly higher.

 

References:

[1] Burch Bottle and Packaging. (n.d.). 1 LITER GLASS LONG NECK BOTTLE. Retrieved on 01.02.2024 from https://www.burchbottle.com/1Ltr-Flint-Long-Neck-28-400.

[2] Islam, M. S., Uddin, M. J., & Alshehri, K. (2018). Plastic waste and carbon footprint generation due to the consumption of bottled waters in Saudi Arabia. Res. Dev. Mater. Sci, 5, 1-3. Retrieved on 01.02.2024 from https://www.researchgate.net/figure/Average-and-median-weight-of-plastic-Bottles_tbl1_324151712.

[3] The Cary Company. (n.d.). Glass vs Plastic: 7 Factors to Consider for Packaging your Product. Retrieved on 01.02.2024 from https://www.thecarycompany.com/insights/articles/glass-vs-plastic-packaging