Why do the words matter?
They get used as if they mean the same thing, yet they don't. Each one makes a different promise about what happens to something once you're done with it, and under what conditions. Once you know the difference, you can judge any claim you come across, ours included.
What does biodegradable mean?
Biodegradable means microorganisms can break a material down into water, carbon dioxide and biomass. That's all it means. The word doesn't say how long it takes or where it has to happen, and given enough time, lots of things biodegrade. The questions worth asking are how fast, and under what conditions.
What does compostable mean?
Compostable is more specific. It means a material breaks down within a set time under composting conditions and doesn't leave anything harmful behind.
In Europe, the benchmark is EN 13432. To pass, a material has to disintegrate within 12 weeks and biodegrade by at least 90 percent within six months, and it's tested for eco-toxicity and heavy metals. The catch: EN 13432 was written for packaging. There's no equivalent standard for footwear yet.
Industrial, home, or something else?
Industrial composting plants control temperature, moisture and airflow so things break down quickly and safely. A compost heap in the garden is cooler and slower, and there's no single international standard for home composting. So something that composts well in an industrial plant won't necessarily break down at home.
SOLK shoes take a third route: our own controlled composting system.
So what does compost-capable mean?
It's the word we use for our shoes, and it means a SOLK shoe can be composted in our controlled composting system. It covers the whole shoe, which is why every material in it, from the leather to the thread and glue, is chosen and tested with that system in mind.
We don't call our shoes compostable, because there's no footwear standard to certify a finished shoe against. Instead, we used the standards for packaging and plastics, DIN EN 13432 and ASTM D6868, as the framework for our own testing. A few components do carry their own certifications, like the fibre in our laces and the material in our lace tips. That doesn't make the whole shoe certified, and we won't claim it does.
What actually happens in our system?
It starts with you sending your shoes back: request a return and we'll send you a label. When they arrive, we shred them, because smaller pieces break down faster. The pieces are mixed with organic matter like grass clippings and coffee grounds, and over the following weeks the temperature climbs above 60°C, hot enough to kill pathogens and speed everything up. We keep an eye on the process and test the finished compost to make sure plants grow safely in it.
What does it mean for your shoes?
First, they won't start breaking down while you're wearing them. Both models are tested for over 1,000,000 step-flex cycles, and composting needs heat, moisture and microbes in controlled conditions that everyday life simply doesn't provide.
Second, they don't belong in your garden. A whole shoe won't break down in a home compost or in the ground on any timeline you could count on.
Third, keep chemicals away from them. Waterproof sprays and synthetic coatings stop a shoe from breaking down, and we can't take treated shoes back.
And when you're done with them, send them back to us. We'll happily take it from there.
Quick answers
Is biodegradable the same as compostable?
No. Compostable means something breaks down within a set time under composting conditions and leaves nothing harmful. Biodegradable, on its own, promises neither a timeframe nor conditions.
Can I compost my SOLK shoes at home?
No. They need to be shredded and composted in our controlled system. Send them back and we'll take care of it.
Are SOLK shoes certified compostable?
No, because there's no composting standard for footwear yet. We test against standards written for packaging and plastics, and some components carry their own certifications.
Will my shoes break down in my wardrobe?
No. Your wardrobe doesn't have the heat, moisture or microbes that composting needs.
Sources
- European Bioplastics, Industrial composting
- European Bioplastics, Compostable plastics and EN 13432