"Compostable" is not a material

A brief that says "we want compostable packaging" has not specified anything yet. Compostable is a claim about what happens after disposal, under conditions that are assumed rather than stated, and those conditions vary more than the materials do.

Two questions that turn the claim into a specification

Composted where? Industrial composting runs at 55–60°C for weeks. A home compost heap in a Bristol winter does neither. A film certified to EN 13432 is certified for the first and says nothing about the second.

Collected how? In most of the UK, packaging in a food-waste stream is a contaminant regardless of what it is made of. The material can be perfect and still end up incinerated because the sorting line has no way to tell.

Replacing what? If the alternative is recycled PET into an established stream, compostable is often worse on every measure that matters. The comparison is never against nothing.

What we ask instead

We ask what the packaging has to survive and where it will actually end up. Those two answers usually eliminate most of a shortlist before a single sample is tested, which is the cheapest testing there is.