“Biodegradable” has become one of the most reassuring words in modern packaging. It appears on coffee cups, shopping bags and food containers, implying a promise: this product is better for the environment because nature will eventually take care of it.

However, biodegradability is not a simple yes-or-no property. It exists in shades, which we can measure.

Biodegradation is a complex process. Microbes and molecules present in an environment such as soil attack a material and digest it, much like what happens to food in our gut.

A material is typically defined as biodegradable if it is digested “well” by the environment in which it is placed. The more mass the material loses during digestion, and the more carbon dioxide it produces, the more biodegradable it is.

Different environments digest materials in different ways. Temperature, sunlight, oxygen, moisture and microbial diversity all influence how quickly materials degrade.

Even the most rigorous testing cannot fully capture the complexity of the real world – but it can help guide our choices.

Biodegradability is relative

In the lab we can simulate environments such as landfill, home compost bins and industrial compost facilities. If we understand in which settings a material breaks down better, we can tell the consumer how to best dispose of it and prevent pollution and other issues.

A material that decomposes quickly in an industrial composting facility may persist for years in the ocean or landfill.

Industrial composting systems maintain elevated temperatures, controlled aeration and consistent moisture. Hot, moist and oxygen-rich conditions generally aid biodegradation but they are not........

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