Five things to know about biodegradable and compostable plastics

For anyone concerned about the impact of single-use plastic on the planet, plant-based plastics that break down and return to the earth seem like a very appealing concept.

But there are a few things to know before you dispose of that compostable coffee cup.

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1. Biodegradable doesn't mean compostable

While biodegradable may be the more commonly understood term, anything made of organic carbon will eventually biodegrade. But this could take years or even decades.

So a product that can be put in industrial compost shouldn't be labelled solely as biodegradable. Compostability is what you need to look out for.

Products that can be organically recycled (ie turned into compost) are strictly controlled by an EU and UK standard: EN 13432.

This requires that 90% of the product disintegrates within 12 weeks, and breaks down breaks down completely to carbon dioxide in six months, under industrial compost conditions. The remaining 10% will be assimilated into the compost and will add to the humus; the standards ensure that nothing harmful can be left behind, including microplastics.

A product that can be organically recycled will have a logo such as the commonly used Seedling logo to to show its compostability.

Listen to the Which? Investigates podcast episode that lifts the lid on plastic and compostables.

2. Compostable doesn't mean it can go in your home compost bin

The certified bioplastics standard only applies to products that are sent to an industrial compost facility. There is no guarantee that products like compostable cups will break down in your compost heap. Some may do but could take a very long time - a year or more.

The exception to this is compostable caddy liners or other thin film bioplastic (made from corn or potato starch) - like the Which? magazine wrapper. Some products will have been tested by a private certification body - TUV Austria - which runs the OK Compost Home scheme.

This means that when lab tested in conditions similar to home compost, these products did break down.

David Newman, managing director of the Bio-based and Biodegradable Industries Association (BBIA), says that film liners marked with an industrially compostable logo will still likely break down in your home compost heap (though how long it take will depend on a multitude of factors), but the manufacturer won't have paid for the extra home composting testing.

If you've got a compost heap in your garden, these are the packaging logos to look out for:

As well as compostable bags, you can also find a good range of home compostable coffee pods. See how some compostable Nespresso-compatible contenders performed in our Nespresso pod taste test.

3. Compostable plastic shouldn't go in your recycling either

Mixed recycling isn't designed for compostable plastics like cups or food trays, either.

It can't be sorted at these facilities and may clog up machinery. Unfortunately, the only real household waste option for your compostable crockery and other similar items is putting them in your general waste.

Most general waste is sent to an energy recovery facility and is usually incinerated. Compostable materials will not have the opportunity to break down but will be burnt along with the rest of the rubbish.

The government is currently consulting on reforms to waste collection to enable the appropriate collection and disposal of industrially compostable items.

David Newman says changes are needed urgently: 'Consumers should be able to send their compostables to industrial composting facilities as part of their household collections. As it stands the situation is leaving consumers understandably confused what to do with compostable plastics'.

For recycling advice, read our guide on how to recycle.

4. You should use compostable caddy liners in your food waste bin

Some councils say it's OK to use plastic liners for your food waste bin (if your council provides a food waste collection service). They may even provide the bags for free. But the Environment Agency plans to remove all non-compostable food material from food waste collections by 2025.

Sites that your food waste is sent to often don't currently distinguish between plastic and compostable liners. Both are removed from the food waste before it's composted or digested in a biogas plant.

But even when this is done, residues of plastic are being found in the compost and digestate at levels which are damaging to the soil.

As things stand, the final material can contain the equivalent of 150 plastic bags per tonne. The Environment Agency says this is not acceptable and must change.

So even if you can use plastic bags in your food waste bin, it's really best not to.

5. It's still better to reuse than recycle

ReLondon, an organisation set up to improve waste and resource management and transform London into a leading low-carbon circular economy, says that because compostable and biodegradable packaging cannot yet be collected for recycling, it is effectively single use.

According to Beverley Simonson, senior advisor at ReLondon: 'It's far better to buy things with no packaging at all. Buying fruit and vegetables loose, or signing up to a veg box, are great plastic-free options; and re-using and refilling your own boxes, bottles or bags are the next best options for replacing plastic packaging.'

But compostable plastics do have an important role to play, particularly in the food service industry. For large events where the disposal of products can be controlled and compostable plastics can all be gathered together, there are great advantages. Food waste and its containers can be collected together and easily organically recycled.