Most "biodegradable" bags won't break down in your home compost pile
Bags labeled "biodegradable" or "compostable" are not the same thing, and most of them won't actually decompose in a backyard compost bin. A bag marked compostable is designed to break down in industrial composting facilities, which reach temperatures of 130°F to 160°F and are actively managed. Your home compost pile, even a well-maintained one, rarely gets hot enough or stays hot long enough to break down these bags. A bag labeled only biodegradable means it will eventually break down somewhere—but "eventually" can mean decades in a landfill, and it may leave behind plastic fragments.
The confusion exists because manufacturers use both terms loosely, and the labeling standards vary by country. In the United States, the most reliable label is ASTM D6868, which certifies that a bag will compost in an industrial facility within 180 days. If a bag doesn't carry this certification, assume it won't break down in your home compost or even in most municipal programs.
Key Takeaways
- Industrial compostable bags require temperatures above 130°F and active management to break down, which home compost piles cannot provide.
- A bag labeled "biodegradable" alone does not mean it will compost; it may take years or decades to break down and may leave plastic fragments behind.
- Look for the ASTM D6868 certification mark to confirm a bag is certified for industrial composting in the United States.
- Most municipal composting programs accept certified compostable bags, but you should check with your local program first because policies vary.
- For home composting, paper bags or no bag at all is the safest choice; putting any plastic bag in your pile risks contaminating the finished compost.
What industrial compostable bags are made of
Most certified compostable bags are made from polylactic acid (PLA), a plastic derived from corn starch or sugarcane. PLA looks and feels like regular plastic, but its molecular structure is designed to break apart when exposed to the heat and moisture of an industrial composting facility. The process takes about 12 weeks at the right temperature.
Some bags are made from polybutylene adipate terephthalate (PBAT) or blends of PLA and PBAT. These materials also require industrial conditions to decompose. The key point is that none of these materials will reliably break down in a home compost pile, even if you've been composting for years and your pile gets quite warm.
Why home compost piles don't get hot enough
A home compost pile reaches its peak temperature—usually 120°F to 140°F—only if you actively manage it: turning it regularly, keeping the carbon-to-nitrogen ratio balanced, and maintaining the right moisture level. Even then, the hot zone is typically only in the center of the pile. Compostable bags need sustained heat of at least 130°F throughout the entire bag, which is difficult to may provide in a home system.
More importantly, most home composters don't maintain peak temperature year-round. In winter or during dry spells, the pile cools down significantly. A bag sitting in a cool section of your pile may not decompose at all, even over several years. You could end up with fragments of plastic mixed into your finished compost, which defeats the purpose of composting.
What happens when you put compostable bags in municipal programs
Many cities and counties now accept certified compostable bags in their green waste or food scrap collection programs. These programs operate at industrial scale, with the temperature control and equipment needed to break down PLA and PBAT. However, not all municipal programs accept them, and policies change. Some programs reject compostable bags because they can jam sorting equipment or because the facility's composting method doesn't reach the required temperature.
Before you put a compostable bag in your curbside bin, contact your local waste management program or check their website. They will tell you whether they accept certified compostable bags and which certification marks they recognize. If your program doesn't accept them, putting a compostable bag in the bin contaminates the entire load and can shut down the facility's equipment.
The difference between compostable and biodegradable labels
Compostable means the material will break down into carbon dioxide, water, and biomass within a specific timeframe under specific conditions—usually 180 days in an industrial facility at 130°F or higher. This is a measurable standard. Biodegradable means the material will eventually decompose, but there is no standard for how long "eventually" is. A bag labeled only "biodegradable" might take 5 years, 50 years, or longer to break down, and it may leave microplastics behind.
Manufacturers sometimes use "biodegradable" as a marketing term because it sounds environmentally friendly but carries no legal obligation. A bag that says "biodegradable" without additional certification is not a safe choice for composting. Look for third-party certifications like ASTM D6868 (United States), EN 13432 (Europe), or AS 5810 (Australia).
What to do with compostable bags if you home compost
If you have certified compostable bags and you home compost, your safest option is to remove the food scraps from the bag and compost the scraps without the bag. You can then dispose of the empty bag in your municipal green waste program if your area accepts compostable bags, or in the trash if it doesn't. This takes an extra step, but it prevents plastic fragments from contaminating your finished compost.
If you want to use bags in your home composting system, use paper bags instead. Paper breaks down reliably in home compost piles and adds carbon to the pile. You can also compost food scraps directly without any bag, though many people find bags convenient for collecting scraps in the kitchen before adding them to the pile.
Checking for legitimate compostable certifications
When you buy a bag, look for one of these certification marks on the packaging:
- ASTM D6868 (United States): Certifies the bag will compost in 180 days in an industrial facility.
- EN 13432 (Europe): The European equivalent, with similar requirements.
- AS 5810 (Australia): Australia's standard for compostable plastics.
- BPI Certified (Biodegradable Products Institute): A third-party certifier in North America that tests bags against ASTM D6868.
If a bag doesn't carry one of these marks, it is not certified as compostable, and you should assume it won't break down reliably in any composting system. Marketing language like "eco-friendly," "plant-based," or "green" is not a substitute for a certification mark.
Frequently Asked Questions
Can I put a compostable bag in my home compost if I wait longer?
No. Even if you wait years, a compostable bag is unlikely to fully break down in a home pile because the temperature never reaches the required level consistently. You will probably end up with plastic fragments mixed into your compost. If you want to use bags, use paper instead.
What if my municipal program says it accepts compostable bags but I'm not sure?
Call or email your local waste management program and ask specifically whether they accept bags certified to ASTM D6868 or EN 13432. Get the answer in writing if possible. Policies vary widely, and putting bags in the wrong program can damage equipment.
Are compostable bags better than regular plastic bags for the environment?
Only if they actually end up in an industrial composting facility. If a compostable bag goes to a landfill or incinerator, it offers no environmental benefit over regular plastic. The best choice is to avoid bags altogether when possible, or use paper bags for kitchen collection and compost the scraps without the bag.
Do compostable bags break down in soil or water?
No. Compostable bags are designed specifically for industrial composting conditions. They will not break down reliably in soil, water, or a landfill. Throwing a compostable bag in the ocean or burying it in a garden will not cause it to decompose.
What should I do with compostable bags I already have?
If your municipal program accepts certified compostable bags, use them for food scraps collection and put the full bag in the green waste bin. If your program doesn't accept them, empty the scraps into your compost pile or green waste bin and throw the empty bag in the trash. Do not put them in your home compost pile.