Why the Colour of Your Yarn Matters More Than You Think
What is the environmental cost of all the beautiful yarn-colours that we can choose from on a daily basis?
When we fall in love with a skein of yarn, it’s usually the colour that gets us first. That deep indigo, soft moss green, or warm terracotta shade can spark the idea of an entire project. But behind every colour is a dyeing process: And that process has a much bigger environmental footprint than most knitters realise. Even for recycled yarn, an additional colouring process usually takes place, and that colouring process isn’t very environmentally friendly - so is recycled yarn even any good?
The hidden environmental cost of dyeing yarn
The global textile industry is responsible for over 3.3 billion metric tons of greenhouse gas emissions every year, making it one of the most polluting industries worldwide. A significant chunk of this impact happens during the dyeing and finishing stage, the moment when raw fibers become the beautifully coloured yarns we love to work with.
The dyeing of yarn has several factors that is harmful to the environment:
Water-intensive (huge volumes of water are used)
Energy-intensive (heating dye baths takes a lot of power)
Chemically intensive, often relying on synthetic dyes and metal-mordants which is metal salts.
Wastewater treatment is important for minimising the environmental impact of dyeing yarns, and when it isn’t properly done - and the wastewater is release into rivers and lakes, the metal salts used as mordants may:
Block sunlight from reaching aquatic plants
Disrupt the natural pH of the water
Introduce toxic by-products that accumulate in fish and move up the food chain
In other words: the colorfast yarn on your needles may have left a long trail of environmental damage before it reached your stash. Even recycled yarns.
And this is where my thesis-topic comes into light. Because there is a whole world of natural dyes and bio-mordants which can be used for the colouring of yarn. Now you may think - But Laura, if such dyes and mordants exist, why isn’t it used by all of the spinning mills and yarn companies? And that is the tricky part and where my research comes into place, because natural dyes and mordants are very tricky to work with.
Natural dyes: beautiful, biodegradable… but complicated
This is why natural dyes have made such a strong comeback in recent years - especially among indie dyers and eco-conscious knitters. You can find hundreds of books describing how to dye your yarn with natural colours. Even though this is great, these books still utilises the common industrial mordants previously referred to as metal salts, which makes the “good intentions” behind doing plant dyeing fall flat.
Unlike synthetic dyes, natural dyes come from renewable biological sources, such as:
Plants (roots, leaves, bark, flowers)
Agricultural or food waste
Microbial or fermentation processes
From a sustainability perspective, natural dyes are appealing because they are:
Biodegradable
Generally less toxic
Compatible with circular economy thinking (waste → resource)
If you’ve ever knit with plant-dyed yarn, you’ll know the appeal: colors that feel alive, nuanced, and deeply connected to nature rather than flat or overly uniform. Furthermore, they are unique and one batch is never the same, meaning you get one of a kind projects.
But here’s the catch…
Wool and other fibers don’t naturally bond very strongly with most plant dyes. Without help, naturally dyed yarns often suffer from poor color fastness, meaning the color may:
Fade in sunlight
Bleed in the wash
Rub off during wear
For knitters, this shows up as:
Colors dulling over time
Dye bleeding when you block a project
Uneven fading in garments that get lots of wear
Mordants: the glue between dye and fiber
A mordant is a substance that helps bind dye molecules to fibers. You can think of it as a molecular bridge between the colour and the yarn.
Traditionally, mordants include metal salts such as:
Alum
Iron
Copper
These work very well. They deepen colour, improve wash fastness, and help natural dyes perform more like modern commercial dyes.
Unfortunately, they come with a major downside:
metal mordants are toxic, non-biodegradable, and persist in wastewater, creating long-term environmental risks.
Researchers are now exploring bio-mordants which is naturally occurring substances that can perform the same job without the environmental harm. These are usually derived from plant based materials and even bio-waste.
These include compounds such as:
Tannins (found in bark, leaves, tea, and many plants)
Flavonoids
Phenolic compounds
From a knitting perspective, bio-mordants are exciting because they:
Improve dye adhesion to wool fibers
Enhance wash, rub, and light fastness
Are biodegradable and less harmful to ecosystems
Imagine a yarn that holds its color through years of knitting, wearing, and washing and without relying on heavy metals. That’s the promise biomordants offer.
If this sounds perfect, you might wonder why all yarn isn’t dyed this way already…
The short answer is consistency and scale. Natural dyes and bio-mordants can vary dramatically depending on:
Plant source
Growing conditions
Extraction method
Season and harvest timing
This variability leads to batch-to-batch colour differences, limited and less predictable colour ranges and challenges reproducing the exact same shade repeatedly. For knitters, that means gorgeous one-of-a-kind skeins, but less reliability for large sweater quantities or restocks. For spinning mills and yarns brands this means unpredictability, scaling issues and major production issues. To move natural dyeing from artisan studios into larger-scale yarn production, researchers are working on standardised extraction methods, better performance testing and applying green chemistry principles without losing beauty or integrity.
As knitters become more conscious of where their materials come from, there’s a growing demand for yarns that are not only beautiful, but ethically and scientifically sound.
This creates a unique opportunity for:
Science-led yarn brands
Transparent communication about dye methods
Honest discussions about trade-offs between perfection and sustainability
Instead of promising “zero impact” (which doesn’t exist), the goal becomes: Better systems, grounded in science, that respect both the maker and the environment. And here comes the fun and exciting part:
That is such a yarn brand that I am itching to start. My love for knitting combined with my engineering expertise could create something great.
The future of sustainable yarn doesn’t lie in rejecting science — it lies in using science differently.
By combining chemical engineering research with entrepreneurial thinking and a love for yarn, fiber science and knitting, it becomes possible to imagine yarns that are:
Scientifically tested
Environmentally responsible and aware
Honest about variability
Designed for knitters, not just manufacturers
I hope that this gives you a perspective and knowledge to make informed choices in the future and to know the impact each purchase makes. Knitting is slow fashion, but yarn is a consumer business. The next time you choose a skein, you’re not just choosing a colour… you’re choosing a story about chemistry, ecosystems, and the future of making.
And that’s a story worth knitting into every stitch.
If you want further reading, you can check out the scientific papers I used for this post:
https://www.mdpi.com/1420-3049/28/16/5954
https://link.springer.com/article/10.1007/s44274-025-00337-0