There is a difference between biodegradable and compostable, although they get misinterpreted and often times misused. The key difference is that biodegradable are any materials that decomposes and breaks down in natural environment, whereas compostable are organic materials that breaks down which can be used for soil as fertilizers. All compostable are biodegradable, however, not all biodegradable are compostable since some biodegradable are made up of non-organic materials like plastics. There are a lot of pet waste bags out there that are both compostable and biodegradable, however, there are also equal amount of pet waste bags that claims they are but aren't. So doing researching on them is critical if you indeed want to help the environment and not fall for their marketing tactics.