What is PBAT?

Our comPOST Packs are made of;

  • corn starch (from corn not fit for consumption)
  • PLA (Polylactide, which is made from waste corn too and other plants)
  • and this other stuff called PBAT (Polybutyrate Adipate Terephthalate).

While PBAT is incredibly biodegradable and will decompose in home compost leaving no toxic residues, it is currently partly derived from petrochemicals, yip, oil. This means it’s not renewable (because the earth’s oil stocks are finite and becoming depleted) and this is why we’re working super-hard to research and test some of the emerging resins which have a higher bio-base (ie. are more made from plants).

Interestingly, it is PBAT that is added to make the product degrade quickly enough to meet the home compostability criteria. To our knowledge there are no bio-based plastics suitable for making courier bags that do not have a binding agent like PBAT in them. There is a lot of research currently to find an alternative, and there has been some success. We are currently supporting our supplier to trial a higher percentage bio-based PBAT.

The irony of this is it can impact the rate of compostability. Unfortunately, when it comes to plant-based inputs there is a trade-off between renewability and compostability – the higher the % renewable, plant-based components the slower it is to compost! As an aside corn cobs, banana skins and avocado skins would not pass the AS5810 home compost test – go figure.

We have, as yet, not found a 100% bio-based, ie. non-oil derived binding agent for our purposes and would love to hear from anyone who has … or purports to have …


  • Rensso

    Hello! Just got a sampler, would you be using GMO-corn?

    • kate

      Hi Rensso, our products are made from PLA (made in America from corn) which is certified not to contain any Genentically Modified material. The other ingredient is cornstarch which is made from non GMO corn stockpiled in case of famine but no longer edible.

  • Aroa

    Hello! Very interesting, thank you for the information. Could you share what’s the % composition of each of the three materials, per bag? Ex. ComPOST packs, black. Thanks a lot!

    • kate

      Hi Aroa, the percentages vary for our different products, but for the comPOST Packs, it’s 5-10% PLA (from corn), 20-25% cornstarch, and the remainder PBAT.

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