A compostable bag is only as good as the compost plant it reaches.

Three words share the bag aisle: oxo-degradable, biodegradable and compostable. They describe three different bags. Only one comes with a test, and that test names a place.

An oxo-degradable bag is conventional plastic with an additive that makes it fragment. Biodegradable says that microbes can break the material down, with no place and no deadline attached. Compostable has standards behind it: ASTM D6400 in North America, EN 13432 in Europe. The European standard asks for at least 90% biodegradation within six months, measured against a reference material, at about 58 °C. The American standard gives the setting in its title: “Municipal or Industrial Facilities”.

Take the plant away and the result changes. The University of Plymouth left bags in open air, soil and sea, and published the results in 2019. After three years in soil and sea, the biodegradable, oxo-biodegradable and conventional bags could still carry a load of shopping. The compostable bag was gone from the sea within three months and still present in soil after 27 months. The bioplastics industry replied that a compostable bag is designed for a composting plant and was never meant to end up as litter. We agree. That is the condition, and it is often not met.

In its 2023 survey, BioCycle counted 14.9 million US households with access to food waste collection, out of more than 100 million. Even there, more than half of curbside programs did not accept compostable packaging (see The Number, below). In Canada, Toronto’s green bin guide says: “Compostable plastic bags are not necessary”. Among composters, the door is opening: 142 of the 200 full-scale food waste composting facilities surveyed in 2023 accepted compostable packaging, 71%, against 58% in 2018.

The recycling bin is no fallback. The Association of Plastic Recyclers design guide for polyethylene film lists PLA, PHA, starch-based polymers and degradable additives as features that “render package non recyclable”. In Quebec, Éco Entreprises Québec adds a penalty to the fee producers pay toward curbside recycling for PLA and other degradable plastics, because they are not accepted in recycling bins and have no adequate treatment process: 20% in 2024, 50% for the 2026 declaration.

There is a place where the compostable bag is the right tool. As of October 2026, Montréal’s food waste collection guide shows most boroughs accepting compostable bags certified by the Bureau de normalisation du Québec (BNQ) in the brown bin, and refusing biodegradable and oxo-degradable bags. There, the bag goes where its standard assumes it goes.

What this changes for you. Before you buy on the word compostable, ask two questions. Does the municipality where the bag will be used collect food waste? Does its program ask for certified compostable bags? Two yeses: ask for the certificate. Otherwise, the word on the box describes a plant the bag is unlikely to reach.