Is silk biodegradable? Can it be composted?

  • Date: May 14, 2022

Silk is used in a variety of products – from medical dressings to bike tires – however, it is most well known for its use in luxurious clothing. Despite being an incredibly durable fabric, unfortunately it will reach the end of its wearable life at some point. If possible, donation of your silk item to charity (or an up-cycler/crafter) is always our top choice. But if this is not an option, is silk biodegradable and can it be composted?

How is silk produced?

Silk is made from natural fibers. The mulberry silkworm – or to use the technical term Bombyx mori – spins itself a silk-like cocoon to live inside when transforming into its adult form. This cocoon is what the silk manufacturers are looking for – and ideally, it needs to be intact. Before the silkworm is strong enough to burst out they apply hot air or even boiling water to the cocoon. This enables them to unwind the it as one long, continuous fiber. But it also kills the little silkworm inside.

Silk is not the most ethical of fabrics (to say the least) out there – leading to it being banned by the online retailer ASOS.

Is silk biodegradable?

Silk, like other natural fibers such as cotton and wool, is biodegradable. This simply means that it can be broken down naturally by micro-organisms. Although, you will need time and patience before you see significant biodegradation. But this shouldn’t come as a surprise – silk is one of the most durable fabrics out there. Incredibly, pound-for-pound silk is said to be stronger than steel.  

Environmental conditions do play a part in the biodegradation of silk. Optimal conditions can see silk broken down in as little as 1-2 years. If it does end up in landfill, it will most likely not outlive you like many other materials.

Can silk be composted?

Composting can be a great way to divert organic items from the landfill pile whilst producing a nutrient-rich compost for your garden. It’s a win-win! Many people assume that if an item is biodegradable, it is automatically eligible for the compost pile. This is not the case – some biodegradable items may simply not contribute to a nutrient-rich compost. Silk ticks both boxes though – it is biodegradable and it can be composted!

There are two main ingredients in compost – ‘brown’ and ‘green’. ‘Brown’ ingredients are carbon-rich whilst ‘green’ ingredients are rich in nitrogen. Silk falls into the ‘brown’, carbon-rich element. As with all composting pursuits, you will need to have an appropriate mix of both types of ingredients to maintain a healthy pile. If you are new to composting you can find out some of the basics here.

Considerations when composting silk..

It is highly unlikely that your silk garment will be 100% pure silk with no additives. Silk tends to be treated with an array of chemicals – from the dyeing process to the finishing process. Regularly dry cleaning your items also adds to the chemical mix. Although the silk will still breakdown, it has the potential to make for a contaminated final product.  For this reason, many people will avoid using the compost on vegetable patches or edible plants. It’s your call.

If you do decide to go ahead, you should be aware that composting silk will take a while – it won’t happen overnight. You can, however, jumpstart the process by ripping the material into smaller pieces. The smaller the better. This gives the micro-organisms in pile a larger surface area to work their magic on.

Other uses for unwanted silk

Before you add silk, or any clothes, to the compost pile you should consider if anyone else can get any use out of the item. If it is still wearable, you could donate it – either to a friend or a local charity – or sell it on eBay. If it is not in great condition, you could still pass it on. Often people can use fabric scraps for their Pinterest-inspired craft projects.

Although, composting is a great way to dispose of organic waste, it is best to get as much use out of it as possible. This especially applies in the case of silk – in most cases, insects were harmed in production. Making the most of this luxurious fabric, in any way you can, is a must.

The bottom line

Although it can take a significant amount of time to compost silk, it will eventually break down and form a great nutrient-rich compost. Ultimately benefitting both your garden and the planet. Although composting is an environmentally friendly way to dispose of waste, we recommend that you consider donating your item first. Lots of resources have been put into its production – maximizing its lifetime is always the first option to consider.