The world biodegradable gets tossed around a lot when talking about eco-friendly diapers. Some websites even offer lists reviewing “biodegradable” diapers, when in fact, many of the options on the list aren’t even marketed as biodegradable, but their packaging just gives off an eco-friendly vibe. For example, lists of “biodegradable” diapers companies often include Hello Bello, Seventh Generation, the Honest Company. This helps make consumers feel like those diapers will break down in the landfill, when in fact, these diapers all use plastic and will not break down for hundreds of years.
That said, some of these companies do take extra steps to make their diapers a little less terrible for the Earth before they hit the landfill; for example, by using some biodegradable materials, sustainably-harvested wood pulp, and keeping them free of chlorine and fragrance.
That all begs the question of whether any single-use diapers are actually compostable.