Whilst a material’s biodegradability is not defined by exact time or location requirements, but depends on the environmental conditions and the material itself, the criteria for compostability are more precise.

A product is considered compostable, if it consists of biodegradable material and within a defined period of time can completely be transformed into CO2, water and biomass without ecotoxic effects. This process is run by micro-organisms under aerobic conditions, which means with the presence of oxygen. With a lack of oxygen, the transformation would slow down or even produce methane.

There is no global standard giving a general and exact definition of a product’s compostability, but there are several international standards specialized on packaging or plastics. Examples are the European standard EN 13432, the international standard ISO 17088 or the American standard ASTM D6400. They differ in some details, but all of them share the following requirements for a successful compostability:

- After a maximum of 12 weeks, at least 90% of the product must be disintegrated at high temperature. Depending on the standard, this temperature varies from 40°C to 70°C.
- A minimum of 90% of the residues arising from this disintegration has to pass through a 2mm fraction sieve.
- No visual contamination.
- After six months at a temperature of 58°C (± 2°C), at least 90% of the organic material has to be transformed into CO2, and the remainder into water and biomass.

Additionally, these standards assess the products’ heavy metals content and, with a plant growth test, evaluate its ecotoxicity. Based on the criteria of EN 13432, a product can be certified compostable. These certifications are not limited to packaging but are applicable to all types of products and confirm their industrial compostability.

Industrial composting differs from home composting in the garden, since the degradation process depends on the temperature as well as the available amount of oxygen and water. For industrial composting, the degradation conditions are optimised by holding them at a constant level and providing very high temperatures, facilitated by human intervention.

This leads to an acceleration of the process in industrial composting facilities, enabling a degradation of materials which would not break down in the garden compost. For instance, there are some bioplastics being suitable for industrial but nor for home composting. Furthermore, a product’s ability to decompose depends on its shape and thickness.

Once more aspect, products labelled or certified as compostable are not to be thrown carelessly into nature but must be disposed of properly.