Compostable or Biodegradable? Please explain.

Compostable or Biodegradable? I’m confused, are you?

Many products use the terms ‘compostable’ and ‘biodegradable’ interchangeably and while they might have a similar intent, the two are not the same. What they are made from, how they decompose and what residue is left behind once they break down are the key differences between the two.

Please explain. 

A compostable product is made from natural plant starch (like corn!) and breaks down into non-toxic natural elements like soil, providing rich nutrients back to the earth.

The key to compostable products breaking down is ensuring the right environment. Compostable products cannot break down in any environment, they need warm temperatures and the right mix of microbial activity (i.e. carbon, air and water). What they don’t need, is any artificial additives to degrade. 

All compostable products are biodegradable, but not all biodegradable products are compostable due to potential toxins left behind by biodegradable products.

To be labelled ‘compostable’ in Australia, the product must be certified Home Compostable AS5810 or Industrially Compostable AS4736 by the Australian Bioplastics Association.

When a product is Australian certified (like Rethink Mailers are!), it means that in compost, they must:

  • Breakdown 90% or more within 180 days, 
  • Disintegrate into less than 2mm pieces within 12 weeks,
  • Have no toxic impact on plants or earthworms,
  • Not have any presence of heavy metals, and
  • The product should be made from at least 50% organic material.  

On the other hand

Biodegradable labelled products can be made from plants or plastic. However these products have added microorganisms that help break down the product fast - and in any environment i.e. landfill, water, soil. While this sounds fab - it’s not, mainly due to two reasons:

  1. Toxins left behind. As the products are generally still plastic they require additives (e.g. metals such as lead and cobalt are added to the plastic) to speed up the degradation process which is then left behind as the product degrades. 
  1. Biodegradable products will often quickly break down into micro-plastics that STILL take thousands of years to disappear. Microplastics are smaller than 5mm (the size of a sesame seed!) and are being ingested by our marine life, often tricking them into believing they don’t need to eat and causing starvation. In addition to marine animals, the average person eats about 70,000 microplastics per year!

There are no certifications required to label a product ‘biodegradable’. Therefore, there is no guarantee that a biodegradable product will degrade within a certain timeframe or that there will be no toxins left behind. 

So, do we pick a side?

In short, yes. 

While biodegradable products can mean any material breaking down in any environment, it doesn’t necessarily mean it is GOOD for the environment. This is due to possible toxins left behind after the product degrades and the creation of microplastics creating a potentially bigger threat to our marine life and our environment. 

Compostable products are required to be certified. This ensures they break down within a certain timeframe (albeit only in specific conditions), are made from organic materials and only leave behind beneficial residual products like fertilizer that nourish and improve soil health and feed plants and grass.

While compostable plastics are not the perfect solution, they are a step in the right direction to reduce the end-of-life impact of plastic on the environment.

compostable vs biodegradable




Oceanwatch Australia:

Easte Waste:

Australian Bioplastics Association: