Which Bag Should We Use

As you fill your cart and get to the front of the grocery store line, you are faced with another choice: Which bag should you use?

If you’ve seen images of plastic bags strewn across the ocean, you might get the impression that plastic is bad for the environment. Surely, a paper bag or cotton tote is a better choice.

But is that true?

Each of these three materials has a unique environmental impact, depending on its carbon footprint, potential for reuse and recycling, and biodegradability. So to fully understand these shopping bags, we need to look at how they’re made, how they’re used, and where they end up.

Let's start with plastic. The typical thin, flimsy plastic bag is made from high-density polyethylene, commonly known as HDPE. Producing this material requires extracting oil from the ground and applying extremely high temperatures. The resulting polymer resin is then transported to a bag-making plant along with other ingredients like titanium oxide and chalk. Here, coal-fired machines melt these materials and spin them into plastic sheets that are then folded into bags. By the time a bag reaches its final destination, it has emitted an estimated 1.6 kilograms of carbon dioxide into the atmosphere. That's the same amount of carbon produced by a car driving more than 6 kilometers.

But the carbon footprint of alternatives is actually much greater. Paper is made from wood pulp, and once you factor in the carbon cost of removing trees from the ecosystem, a single paper bag emits around 5.5kg of CO2. Meanwhile, growing cotton is an extremely energy- and water-intensive process. Producing a single cotton tote bag emits an estimated 272kg of CO2.

When we compare carbon footprints, plastic bags are the clear winner. But the environmental impact also depends on how the bag is used. Reusing or recycling these bags can significantly offset their environmental impact by reducing the need for new products.

To quantify this offset, we can divide the bag’s carbon footprint by the number of times it is reused. For example, if a typical paper bag is reused three times, its net impact is lower than a single-use plastic bag. If a cotton tote bag is reused 131 times, its carbon footprint will also be reduced.

Of these three options, durable fabric tote bags are most likely to be reused. There is evidence that paper bags are quickly discarded because they tear easily. This problem also plagues high-density polyethylene plastic bags. But even if they are designed not to tear, their widespread use makes it easy to dismiss them as disposable items. Fortunately, researchers estimate that 40% of HDPE bags are reused at least once for trash disposal.

Recycling these bags can also offset their carbon footprint, but this isn't universally possible with every material. Many countries lack the infrastructure to effectively recycle plastic bags. Cotton tote bags may be harder to break down and process, but since they are often reused over long periods of time, they are least likely to end up in landfill.

If these bags are not recycled, a third factor in calculating environmental impact comes into play: degradability. Because HDPE bags are heat-resistant and do not dissolve, they remain around long after we are done with them. Once plastic is partially broken down, it can circulate in the ecosystem for hundreds of years. Cotton, on the other hand, degrades significantly within a few months, and paper bags completely decompose in as little as 90 days.

So, which bag should you use?

It turns out that the most eco-friendly bags have characteristics of several of the materials we discussed. They are as durable and reusable as cotton but are made from plastic and have a lower carbon footprint than cotton or paper. Made from polyester, vinyl, and other tough plastics, these sturdy shopping bags are used around the world. What's more, they should last a lifetime, making them the best choice for the planet and your groceries.