Knowing the difference can influence purchasing decisions.

Which is better, a biodegradable product or one that is compostable? The short answer is that the compostable product is the better choice. A product marketed as natural and biodegradable - like plastic garbage bags made from sugar cane - may be neither; especially if it ends up in a landfill where pretty much nothing ever biodegrades.

What makes something biodegradable?

One way to define whether something is biodegradable is if after some metabolic or enzymatic processes, the molecular structure of that thing can broken down. There is no limit on the length of the process or what’s left after completion. The time frame for biodegradation can last from several days to millions of years.

Dinosaurs are biodegradable. Yet, we still run across their bones from time to time. Is it any surprise then when archeologists tunnel through landfills (talk about a field of study with some job security) they often uncover 50 year old newspapers that look hot off the press and even guacamole still good enough to eat.

Just because something can biodegrade, doesn’t mean that it actually will in a reasonable amount of time.

Does biodegradable mean environmentally friendly?

Most things, especially newspapers and guacamole, if left out in the open will biodegrade over time. The sun and weather break down newspapers and a tribe of wild nacho chips would finish off the guac.

But even if left out in the open, things that are supposedly “biodegradable” may not do much degrading. “Biodegradable” plastic bags would seem to be an eco-friendly solution to the blight of plastic pollution and waste. But check this out, even after three whole years in the ocean, scientists have found that bags billed as biodegradable can still hold a load of groceries.

Biodegradable is a nebulous marketing term with plenty of wiggle room. Something can sound eco-friendly without having to be verifiably proven to be less harmful to the planet.

In short, biodegradable products are like herbal supplements - they haven't been rigorously tested to do what they are purported to.

What is compostable?

If you live someplace where leaves fall off trees you may have started a compost pile some point in your life. Many people keep special bins for yard and food waste that are perfectly suited to break down organic matter and turn it into a rich soil that's good for plants. Under normal conditions it takes about 6 to 12 months to turn leaves into compost.

In theory, compostable products behave in the same way.

FACT: to be labeled compostable, no toxic materials can persist after an item has been broken down. Objects labeled biodegradable do not have this requirement.

If you're interested, you can check out our guide to composting with the Eden Project's Catherine Cutler.

What makes a product compostable?

For a product to be termed “compostable” certain legal obligations have to be met. This is usually a recipe for the type of material. It dictates the duration of time needed to decompose and the specific conditions needed for decomposition to take place. One example is ASTM D6868, it’s the recipe that packaging that is designed to be composted (including plastic coated paper and board) should comply with if it wants to display that certification.

Compostable products are better for the environment, right?

Yes and no; maybe and it depends. Some “compostable” things might not compost the way you think (remember that guacamole?). Sometimes the composting recipe has requirements that only exist in industrial composting facilities.

Let’s looks at leaves again. In some places, municipalities collect bagged up leaves. The leaves are transported to compost facilities where they are composted on an almost industrial scale (for leaves at least). These leaves receive more attention than the average backyard compost heap and since the process is more controlled, it will produce a more consistent result.

Similarly, many compostable products - like the majority of bioplastics - are engineered to biodegrade or be compostable in a managed process dedicated to that kind of compostable waste.

This has lead to confusion but things are getting better. In the EU products can be labeled OK Compost Home or OK Compost; the latter designating that the product needs a commercial or municipal composting facility to break down.

Are compostable plastics recyclable?

Yes, but. Oftentimes bioplastics can’t be recycled with other plastics — they can ruin batches of recyclable plastic, degrading the product until it becomes unusable.

Are compostable plastics better for the environment?

Again, it depends. Ethylene, the raw material for all packaging plastics, is derived from either natural gas or crude oil. These carbon sources took millions of years to accumulate and are not renewable. Producing and refining ethylene requires massive amounts of energy which could be better used elsewhere.

Using plants as the carbon source is much more sustainable when compared with petroleum or natural gas. Plant based plastics can be carbon-negative which is a massive improvement however it still needs to be collected and recycled properly.

But plastic is still plastic.

Plastic pollution whether it’s bags in trees, or microplastics in water and food, is still pollution no matter the ultimate source, and can cause a lot of damage to ecosystems and even us.

Not using plastic when it isn’t necessary is the best way forward.

Dispose of things in the right place

The deep, anoxic waters of the Black Sea have perfectly preserved wooden ships that sunk millenia ago. Banana peels locked in landfills last for decades. Bottles turn into sea glass in 20 to 30 years. Trees turn into petroleum after several million. The time something takes to break down and what is left behind depends on a lot of different things.

If there’s no catalyst to start the change - air, microbes, temperature, etc - or if something is disposed of in the wrong place, even things made from natural materials can persist in the environment.

Try to make LESS trash. For things you do buy, look for alternatives to plastic. Products made from recognisable materials with little packaging are best. For more info on what to look out for, check out our guide to products you might think are compostable but aren't.

The compostable mobile case

When we designed our circular mobile cases we made sure that, if you don't want to send them back to use to be recycled, then they can be composted in your back garden and safely returned to the biosphere from which they came (they're made from plants, you know).