What Are Compostable Bags? The Degradation Difference Between Them and Ordinary Plastic Bags Is Surprisingly Big

Walk into a grocery store or a local market, and you might notice more bags labeled “compostable” these days. But what does “compostable” really mean? It’s not just a fancy word for “eco-friendly”—it’s a specific term that describes how a material breaks down over time. Unlike ordinary plastic bags, which can linger in the environment for hundreds of years, compostable bags are designed to fully decompose, leaving behind nothing harmful. Let’s break down what compostable bags are, how they work, and why their degradation process is so different from regular plastic.

First, let’s clear up what a compostable bag is. A true compostable bag is made from organic materials—think plant-based fibers like cornstarch, sugarcane, or potato starch, sometimes mixed with small amounts of natural polymers. These materials are chosen because they can be broken down by microorganisms, like bacteria and fungi, in the right conditions. But here’s the key: “compostable” doesn’t mean it will decompose anywhere. It needs specific environments—usually industrial composting facilities, where temperatures stay between 55°C and 70°C, there’s plenty of moisture, and oxygen is circulated. In these settings, the microorganisms feed on the bag’s organic components, breaking them down into water, carbon dioxide, and a nutrient-rich material called humus. Humus is great for soil—it helps plants grow, which closes the loop on the bag’s life cycle.

Now, compare that to ordinary plastic bags. Most regular plastic bags are made from polyethylene, a synthetic material derived from petroleum. Polyethylene is designed to be durable—so durable, in fact, that microorganisms don’t recognize it as food. When you throw a plastic bag away, it might end up in a landfill, where it’s buried under layers of waste. Landfills are dark, dry, and lack the oxygen and heat needed for decomposition. In that environment, a plastic bag can take 200 to 1,000 years to break down—and even then, it doesn’t fully disappear. Instead, it breaks into tiny pieces called microplastics, which seep into the soil, wash into rivers and oceans, and can end up in the food chain. Fish eat microplastics, birds mistake them for food, and eventually, these tiny particles can make their way into the fruits, vegetables, and seafood we eat.

The difference in how quickly they break down isn’t the only surprise—what they leave behind matters too. When a compostable bag fully decomposes in a composting facility, it turns into humus, which is a benefit to the environment. It adds nutrients to soil, improves soil structure, and helps retain water. There’s no toxic residue, no microplastics, just something that helps plants thrive. Ordinary plastic bags, on the other hand, leave behind those microplastics and can release harmful chemicals as they slowly break down. These chemicals can contaminate soil and water, harming plants, animals, and even humans over time.

You might be wondering: Can I just throw a compostable bag in my backyard compost pile? It depends. Backyard compost piles rarely reach the high temperatures needed for compostable bags to break down quickly. In a home compost pile, a compostable bag might take months or even years to decompose fully—much longer than in an industrial facility. If you want to make sure your compostable bag breaks down properly, check the label. Many compostable bags are certified for industrial composting, which means they’ll decompose within 180 days in a facility. Some newer types are also certified for home composting, so they’ll break down in your backyard pile too—just look for that “home compostable” label.

Another common mix-up is between compostable bags and biodegradable bags. But they’re not the same. Biodegradable bags can break down over time, but they might leave behind microplastics or toxic residues. Compostable bags, on the other hand, are a type of biodegradable bag—but they have a stricter standard: they must break down completely into non-toxic materials that benefit the soil. So every compostable bag is biodegradable, but not every biodegradable bag is compostable. That’s an important distinction when you’re trying to choose a more eco-friendly option.

Why does this matter? Because plastic pollution is a huge problem. Every year, millions of plastic bags end up in oceans, forests, and landfills. They clog drains, harm wildlife, and contribute to long-term environmental damage. Compostable bags offer a way to reduce that harm—if they’re used and disposed of correctly. For example, a compostable produce bag used for fruits and vegetables can be thrown into a compost bin (or taken to an industrial compost facility) after use, where it will break down and help grow more food. An ordinary plastic produce bag, though, will likely end up as waste that sticks around for centuries.

Of course, compostable bags aren’t a perfect solution. They still require resources to produce—growing corn or sugarcane for the starch uses water and land, for example. And if they’re thrown into a regular trash bin instead of a compost bin, they’ll end up in a landfill, where they won’t decompose properly (just like plastic bags). But when used right, they’re a much better choice for the planet than ordinary plastic.

The bottom line is this: Compostable bags are more than just a “greener” alternative—they’re a material that works with nature, not against it. Their ability to fully decompose into nutrient-rich humus sets them apart from ordinary plastic bags, which leave behind lasting harm. By understanding what compostable bags are and how to use them, we can make small choices that add up to big changes for the environment. Next time you reach for a bag, whether it’s for groceries, produce, or trash, consider picking a compostable one—and make sure it ends up in a compost pile or facility. It’s a simple step, but it’s one that helps keep our planet cleaner for years to come.