What is the difference between biodegradable and compostable?

Compostable has a defined meaning; biodegradable, on its own, has almost none. That asymmetry is why the two words appear together so often on packaging and why the distinction is worth knowing.

Biodegradable means only that something will eventually be broken down by microorganisms. It sets no time limit and specifies no conditions. A material that takes decades and leaves fragments behind still technically qualifies. Because the claim is so weak, it is a common vehicle for misleading marketing.

Compostable is a certified standard. A compostable product must break down within a defined period, under defined conditions, into material that supports plant growth and leaves no toxic residue. Certification marks exist for this, and a genuine claim will reference one.

The critical detail is which conditions. Most certified compostable packaging requires industrial composting: sustained high temperature, controlled humidity and mechanical turning. A home compost heap does not reach those temperatures, so an industrially compostable item may sit in a garden bin essentially unchanged for years. Home compostable is a separate, stricter certification, and much rarer.

This creates a practical problem. If your area has no food and garden waste collection that accepts packaging, a compostable item has nowhere to go and ends up in general waste, where in landfill it may break down anaerobically and produce methane. In that scenario it is not an improvement over conventional plastic, and arguably worse.

Compostable items should also not go in plastic recycling, where they are contaminants that can weaken recycled material.

The honest position is that these materials work only where matching collection infrastructure exists.