What are the differences between Biodegradable and Compostable?

Biodegradable versus Compostable Glossary

What are the differences between “biodegradable” and “compostable”?

We think it’s easiest to think of biodegradable and compostable as rectangles and squares, respectively; all compostable items are biodegradable, but not all biodegradable items are compostable. These are very, very broad terms — biodegradable just means that items break down into organic matter, typically in a three-to-six-month window. Compostable, on the other hand, is when organic material degrades into a soil-filled environment resulting in a nutrient-rich substance called humus. No no, not hummus...humus, which contributes to soil’s ability to retain moisture and nutrients. 

Do compostable products biodegrade?

To be clear, when that compostable cutlery and alternative-material packaging says it’s compostable on the packaging, that means it can biodegrade. However, in order for it to actually biodegrade it needs very specific conditions. So, when you read “compostable”, ask yourself where

What kinds of products are compostable?

Compostable single-use items are all the rage – including everyday items from cutlery and straws to bottles of water. These products are often made from biodegradable bioplastics, meaning plastic that is not made from fossil fuels, but rather from an organic material, like cornstarch. Remember, some bioplastics are low-degrading or nondegradable, meaning that they can only break down in specific conditions, like at high temperatures. Rectangles and squares, folks. 

How do products compost?

Let’s take, for example, a cornstarch-based bioplastic fork. When that fork goes into an industrial composting facility (more on this below), the bioplastic is put into specific conditions (i.e. temperature and oxygenation) that help it break down into small fragments (that aren’t microplastics because it’s made from organic material). Those fragments can then be digested by bacteria, and, voila, the fork biodegrades. 

Are there any certifications I should look out for?

The Biodegradable Products Institute has a certified-compostable standard to ensure that products are meeting a threshold of biodegradability (often shown on packaging as BPI-certified). The certification program was launched in 1999 through a collaboration between scientists, resin producers, and the composting industry. It ensures that if the product with this label is disposed of in an industrial composting facility, it will biodegrade completely and quickly. That approved threshold is defined as products that will biodegrade through the same process and timeline as for yard trimmings and food scraps – booyah! This link from the Biodegradable Products Institute can help you check to see if a product that claims it is compostable is actually certified. 

Remember, even if a product is certified-compostable, it doesn’t change the fact that we simply do not yet have the widespread infrastructure nationwide to support increased composting of single-use items (we’re talking about needing to sort, transport, and actually compost these materials). 

What happens if I incorrectly dispose of a compostable product (aka throw it in the trash)?

The environmental benefit of composting is only realized when items are disposed of properly. To effectively do their decomposition work, organics require oxygen, specific levels of light, and bacteria to break down. When buried under layers of other synthetic materials (aka in a landfill), organic materials can’t breathe. Instead, these materials release methane, an extremely harmful and potent greenhouse gas that does a number on global warming (its GWP is 28, which means it’s that many times more potent than carbon dioxide over a 100-year period). 

Remember, those “compostable” materials often require industrial composting facilities to actually break the product down. This means we can’t just toss it into our at-home composting bin. Industrial composting facilities have very specific temperatures, humidity and moisture levels, as well as availability and concentrations of oxygen. Unfortunately, this means that if the “compostable” fork you got with your salad at the supermarket ends up in your at-home composting bin, it will not properly degrade, and could increase the amount of methane it releases as it degrades. Yikes.

Alternatively, if you toss that bioplastic into the recycling bin along with your plastic cup, because it doesn’t feel right to toss it in the trash because it looks like plastic, you could end up contaminating an entire batch of otherwise recyclable goods. Why? Because compostables are inherently made out of organic materials, which is a contaminant in the recycling system. That batch of recyclables then ends up in a landfill where the bioplastic doesn’t break down properly.

Still want to learn more? Check out some of our favorite references: