What's More Sustainable, Glass Or Aluminum?

Consumers are increasingly paying attention to the sustainability of the products they purchase, including the packaging in which products get sold. From established global Consumer Product Goods (CPG) firms to new Direct-To-Consumer (DTC) startups, brands are making an extra effort to make their products and operations as environmentally friendly as possible. 

Some of those efforts are more sizzle than greenhouse-gas-generating steak; others are straight-up greenwashing.

Despite having many advantages over other materials, such as cost, weight, and durability, many firms are ditching or reducing their use of synthetic plastics due to the material’s significant and long-term environmental damage. Plastics typically get made from petroleum, the extraction of which is itself harmful to the environment. In addition, plastic trash that enters the environment sticks around for hundreds of years, slowly leaching small, microscopic bits as it bobs and decays in our oceans, waterways, and landfills.

That's why a few brands have chosen to eschew plastic for some of the most reliable packaging materials around. You might have even heard of them?

That's right—glass and aluminum. Each material has its unique advantages and disadvantages compared to plastic, but all are more recyclable than plastic. But which is better, and how can that be assessed by both brands and consumers looking to replace single-use plastic bottles?

Now that plastic is stinkier than a skunk at a garden party, consumers base their purchases on a product's sustainability and ecological characteristics. For some liquids and beverages, especially carbonated drinks, durable materials like glass or metal are required to safely protect the product during transport, sale, and storage. Both materials are described as “infinitely recyclable,” meaning that bottles made from either material can be collected and made to use new ones with no degradation with each cycle.

Glass and plastic bottles can also get made to be translucent, allowing consumers to see the product inside. Though glass bottles can get made with intricate forms and shapes, similar effects can be made at a significantly lesser cost using plastic. A bottle's material can signal particular attributes to the consumer, which creates expectations that can influence taste. Glass can project a premium quality, and when considering perception, a luxury or upscale brand might prefer glass to aluminum.

Other elements besides recyclability factor into a material’s sustainability, of course. But what they are isn't as straightforward. Calculating the totality of a given piece of packaging’s environmental impact needs to take into consideration other aspects, such as the impact mining, manufacturing, and transport have on the environment. The sustainability of a package, especially those made with recyclability in mind, also depends on whether consumers are actually recycling it.

According to Paul Foulkes-Arellano, founder of Circuthon Consulting, a firm that assists businesses in setting and achieving circularity goals, the factors to consider when evaluating the sustainability of a packaging material includes the mix of energy source, the amount of used material collected, level degradation with every cycle, and the toxicity of the recycling process for the final product.

“If we are being really geeky, and we have to be, we should consider the energy cost in gigajoules per ton. Glass and metals perform well compared to papers and plastics on this,” Paul said. 

How or if these factors get included in a Life Cycle Assessment (LCA) varies by study, and the complexity of measuring the environmental impact of different materials can make broad and definitive conclusions difficult. Even individual examples of packaging made from the same material can vary in sustainability based on the kind of energy used to make it or the distance the raw material traveled to manufacturing plants. The efficiency of individual factories will also factor into the amount of energy and raw materials needed to produce and thus impact the sustainability bona fides of the final product.

The industries that make the materials and the packaging support LCA studies on their products, of course, and unsurprisingly, those studies often have conclusions favorable to their materials. That further complicates heads-up comparisons of one material over another.

One study conducted in the UK and published in the journal Detritus compared several alternatives to plastic bottles for various categories of beverages, including milk, juice, and pressurized drinks. The study compared virgin and 100% recycled glass and aluminum as well as Tetra Pak cartons against virgin and recycled PET. They scored each material on several environmental factors: acidification potential, climate change, depletion of abiotic resources, eutrophication, freshwater aquatic ecotoxicity, human toxicity, ozone depletion, photochemical oxidation, terrestrial toxicity, and marine aquatic toxicity. 

Taking into account recycling and other end-of-life factors, researchers found Tetra Pak cartons beating other options when it comes to non-carbonated liquids. Aluminum, however, was the most sustainable alternative to plastic (though we should note that Tetra Paks aren't universally accepted by US curbside collection and are confusing to recycle). Despite glass being infinitely recyclable, even PET bottles had a less overall impact on the environment.

But don't pump the brakes on glass just yet.

“The biggest misconception in glass is that there is no sustainable innovation happening—which is not the case,” explains Foulkes-Arellano. “Encirc and Glass Futures are piloting the world’s most sustainable glass bottles by pioneering the use of biofuel, a much more sustainable fuel source than those traditionally used by the glass sector, and is thought to be able to reduce carbon emissions up to 90% when compared to fossil fuels. Alongside this trial, Encirc will use up to 96% recycled glass to create the new bottles, further reducing the carbon footprint.”

Misunderstandings surrounding aluminum also exist, complicating a straightforward comparison between different packaging. Aluminum is lightweight and strong—just like plastic—while being a more circular alternative. However, the material’s sustainability relies on consumers recycling their aluminum cans and bottles, as bauxite mining is pretty awful for the environment and the organisms—including humans—that live around the mine.

“There is a misconception, spread by the plastics industry, that aluminum is heavier than plastic—which is entirely untrue—an aluminum can is now lighter than a plastic bottle. Plastics packaging promoters conveniently forget to mention the weight of the lid and the label,” said Foulkes-Arellano.

To take advantage of the sustainability attributes of non-plastic alternatives like glass and aluminum, we must have efficient and effective collection programs in place. In Europe, consumers recycled just over 76% of aluminum cans or 457,000 metric tons of metal. That saved the equivalent of 3.7 million metric tons of CO2, about the same amount of greenhouse gas generated by a mid-sized European city of about 400,000 people. The US recycles about 46% of aluminum cans.

For consumers that want to spend according to their ecological priorities and brands looking to transition away from plastic packaging, making a sustainable comparison between different materials can be nearly impossible. Under the current single-use bottle economy, recycling is critical in mitigating the environmental impact of the production and use of packaging. Plastic, even when recycled, will eventually degrade to a point where it can no longer get reused and become a centuries-long pox on the planet and its inhabitants. 

Discarded aluminum and glass don't have the same toxic impact on the environment. But the mining of raw materials such as bauxite and silica, as well the manufacturing of the final product, requires considerable energy and is environmentally harsh.

So, what’s more sustainable, glass or aluminum?

Turns out the answer isn’t so simple. “Sustainable,” and all of its umbrella definitions, isn’t just about recyclability but also other factors like collection rate, the energy required to create the original substrate, and the energy required to recycle it, the type of energy used, the environmental impact of mining the raw material, as well as the impact of recycling it. Furthermore, LCA studies are not uniform and get funded by industries and companies vested in particular outcomes. There isn't a slamdunk answer for consumers and brands looking to make decisions based on a sustainability ranking.

"There's no single answer,” said Foulkes-Arellano.

It really depends on your local recycling capacity and collection rates—which vary from city to city, state to state, and country to country. In the end, it might be best to throw your hands up and say, well, they're both better than plastic.

Dieline Verdict: They both have advantages. Stop using single-use plastic.