Are all compostable bags the same?

Alas, no. Silly us, we thought all compostable bags were alike, and that we should buy based on price (and reviews). Turns out, we received an email from our curbside composting service saying that we can only use certain “CMA certified” bags, and they identified four specific brands (and sizes).

Checking further, this isn’t unique to our composting service.

There are several types of compostable bags, and some may not meet the specific requirements for composting in your particular composting facility.

What are the compostable certifications, and why don’t all compost bags meet those standards?

There are a couple of different compostable certifications in use.

Commercial composting facilities typically require bags to be certified as compostable according to specific industry standards (ASTM D6400 (US) or EN 13432 (EU). These standards ensure that the bags will break down under the conditions found in industrial composting facilities, including high temperatures and microbial activity, and within established timeframes. BPI certification, by the Biodegradable Products Institute, is the primary certification awarded in the U.S., to products that breakdown in a lab, under the specified control conditions.

However, in practice, commercial composting facilities don’t all use the same composting techniques and processes. Also, not all “certified” compostable items will break down as fully or quickly as needed. (Yes, there is some misleading marketing of composting bags, too.)

Since these processes vary, commercial processors may have narrower requirements for what they can accept. So, although the traditional certification standards measure compostability based on laboratory conditions, they do not guarantee expected results given actual field conditions at any given compost facility. If the raw materials are not completely converted to clean compost, the finished product may contain contaminants, which means an inferior (and less sellable) product, or worse – the entire batch could end up in a landfill.

So, it’s important for compostable products to be evaluated in real-world testing, in the field, for each of the standard processes in use. The additional certification, given by CMA (Compost Manufacturing Alliance), ensures that the tested materials will break down properly in the field, in the expected timeframe, for each tested composting process. Commercial composters can use this standard to ensure that the compost they produce will meet their quality standards, without leaving chemicals or residue that their customers do no want.

Additionally, some composting facilities may only accept certain types of compostable bags, such as those made from specific materials like cornstarch or biodegradable polymers.

How do you determine which compost bags are accepted by our composter?

It’s important to check with your local commercial composting facility to see if they accept compostable bags and if there are any specific requirements or restrictions. Also note that some commercial composters limit the size of the compostable bags they’ll accept.

What are the rules for commercial composting in Colorado?

Where we live, along the Colorado Front Range, the primary commercial composter is A1 Organics. They specifically identified four compostable bag manufacturers, that meet their acceptable standard, CMA. They also limit the compostable bag size to up to 3 gallons.

Note that these rules apply specifically to A1 Organics’ commercial composting service along the Colorado Front Range and probably are different for other composting facilities.

Here are the four specific compostable bags that A1 Organics will accept as of April 2023 (all limited to a maximum size of 3 gallons):
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BioBag – The Original Compostable Bag, 3 Gallon 100% Certified Compostable Kitchen Food Scrap Bags. This particular package contains 100 bags.		Buy on Amazon
Certified Compostable Bag – 2.5 Gallon Extra Strong Leak, Puncture and Tear Resistant Food Scraps Bin Liners, Pack of 90		Buy on Amazon
Natur-Bag – Small Food Waste Compostable Bags for Food Scraps. – 3 Gallon. This package contains 25 bags, but there are other package sizes available.		Buy on Amazon

BIOSAK – These bags appear to only be available in tall kitchen trash can size – 11 gallon, in the U.S. You can find the 3-gallon size at Amazon Canada. More sizes are available in Canada, but we couldn’t find the 3-gallon bags available in the U.S.

What to do with compost bags we can’t use?

In cases where a composting facility no longer accepts compost bags that you have on hand, what can you do? Well, we’ll just repurpose ours as regular trash bags for our kitchen, for food wrappers and such that need to go in the trash. Since we no longer use the single-use bags from the grocery store, we do need some small bags for that “wet trash”, and these compost bags will work fine.

Please note that you can’t put any compost bags in your recycling bin. The recycling bin can only contain recyclable paper products and plastic containers, and composting bags are not recyclable. In fact, compost bags would contaminate the recycling stream.

More info

Did you know that some paper plates are compostable? Many are not. And, there are some very interesting paper alternative compostable plates. Check it out.