Degradable, biodegradable, compostable bags – what’s the difference?

With so many claims of degradable, biodegradable and compostable, how do we know which bags to use?


Go in the waste to landfill bin

Degradable describes where the ordinary plastics are treated with additives, usually consisting of heavy metals to cause the material to disintegrate over a number of years.  

  • Causes of the degradation: sunlight, time, water, chemicals, micro-organisms
  • Time to degrade: varies a lot, but generally a long time
  • Residue: possibility of residues is high

Degradable bags are still toxic and are also likely to survive long enough to be a threat to animals – and because they break down into tiny pieces, smaller animals could eat them that would otherwise be unable to consume the whole, non-degradable plastic bags.


Go in the waste to landfill bin

Biodegradable plastic bags are a specific type of degradable but that still doesn’t mean they are ok to compost.

  • Causes of the degradation: mainly naturally occurring micro-organisms such as bacteria and fungi
  • Time to degrade: can vary from days to months to years depending on the material & environment
  • Residue: depends on the nature of material, time and the environment


Compostable bag logoGo in the waste to green organics bin

Compostable plastic bags are a specific type of biodegradable. The main differences between them are; how fast they break down; how small the particles are that they break down into, and the toxicity of these particles.

For plastic to be considered compostable, it:

  • must be able to break down at the same rate as paper
  • needs to look like compost
  • should not produce any toxic material
  • should be able to support plant life

To meet the Australian Standard for compostability AS4736, bags need to meet the following criteria:

  • disintegrate into less than 2mm pieces in compost within 12 weeks 
  • no toxic substances should be formed during composting
  • hazardous substances such as heavy metals should not be present
  • bag should contain more than 50% organic materials
  • Causes of the degradation: microbiological, in a controlled environment
  • Time to degrade: days to weeks
  • Residue: no toxic residues left