Using bags for the 32-gallon bins is optional; you can use any container or kitchen pail to transfer the contents to the 32-gallon bin.
The most environmentally friendly choice is not to use a bag for your bin/ pail, but some people find it easier to manage their food scraps with a bag. If you choose to use a bag, paper is more environmentally friendly than compostable plastic; because paper can be composted along with your organic food waste. This also allows you to save the cost on compostable bags.
BPI certified compostable bags can also be used for lining your bins, but compostable bags require higher temperatures and longer processing times than food scraps to compost. At the Prairie Green composting facility where the organics are taken to be composted, these bags are often screened out as they do not break down well.
We noticed that most of our residential customers are using smaller bags for their interior pails, so lining the 32-gallon bin with another bag is not necessary.