I'm a bit of a fabric nerd. Always have been.
While other people at fashion school were obsessing over silhouettes and mood boards, I was in the textile lab asking questions about fiber structure and dye penetration rates. Not because I was trying to be different—I just genuinely found it fascinating coming from a science background.
That curiosity has only deepened over the 11 years I've been building Rosenberries. Because here's what I've learned: the most important decisions we make about sustainability happen at the material level, long before a garment is even cut.
And nowhere is this more critical—or more hidden from consumers—than in the dyeing process.
What actually happens when fabric gets coloured
Let's start with the basics, because I think most people don't actually know what "dyeing fabric" means beyond the conceptual level.
Dyeing is a chemical process where colorant molecules bond with textile fibers. The goal is to get those molecules to penetrate the fiber structure and stay there permanently; or at least long enough that your jeans don't fade after one wash.
There are multiple ways to achieve this and the method used depends on the fiber type, the desired colour and (crucially) how much the manufacturer cares about environmental impact.
Conventional dyeing: the dirty truth
Traditional textile dyeing is one of the most polluting processes in fashion manufacturing. I'm not being dramatic; the numbers are staggering.
The global textile industry uses approximately 1.7 million tonnes of dyes annually. Of that, an estimated 10-15% ends up in wastewater because the dye doesn't fully bond with the fabric during processing.
That wastewater contains:
-
Heavy metals (chromium, copper, zinc from mordants that help dyes bond)
-
Toxic chemicals (formaldehyde, aromatic amines, some carcinogenic)
-
Salts (used to push dye into fibers)
-
Alkalis and acids (to prep fabric and fix color)
In countries with weak environmental regulations, this wastewater often goes directly into rivers. Literally. I've seen photos from textile regions in Bangladesh and India where rivers run bright blue or red depending on what's being dyed that week.
The human cost is immediate. Communities downstream drink that water, fish in it, and irrigate crops with it. The environmental cost is long-term; ecosystem disruption, soil contamination, bioaccumulation of heavy metals in the food chain.
The chemistry bit (stay with me)
Different fiber types require different dyeing approaches:
Natural fibers (cotton, linen, hemp): Usually dyed with reactive dyes or direct dyes. Reactive dyes form a covalent bond with the fiber; meaning for a very strong chemical connection. This is good for colourfastness (your colour doesn't fade easily) but requires high water temperatures, lots of water and chemical auxiliaries to make it work.
Synthetic fibers (polyester, nylon): Usually dyed with disperse dyes at very high temperatures (130°C+) under pressure. This process requires less water than cotton dyeing but uses more energy and often involves chemical carriers that help the dye penetrate synthetic fibers. Some of these carriers are nasty; potentially toxic and difficult to remove from wastewater.
Protein fibers (wool, silk): Usually dyed with acid dyes in acidic conditions. Generally less environmentally harmful than synthetic dyeing but still requires careful wastewater management.
The problem isn't necessarily the dye molecules themselves; it's everything else needed to make them stick: the mordants, the leveling agents, the pH adjusters, the salt, the heat, the water volume.
What "sustainable dyes" actually means
When brands claim "sustainable dyeing," what are they actually talking about?
There's no single definition, which is part of the problem. But generally it involves one or more of these approaches:
1. Low-impact dyes
These are synthetic dyes (usually fiber-reactive) that require less water, lower temperatures and fewer chemical auxiliaries than conventional dyes. They also have higher fixation rates; meaning more of the dye actually bonds with the fabric instead of washing away.
The Oeko-Tex Standard 100 certification covers this. It's not perfect, but it's a decent baseline for dyes that don't contain harmful substances.
At Rosenberries, we use low-impact fiber-reactive dyes for our cotton and cotton-blend pieces. They cost more (about 20-30% more than conventional dyes) but the fixation rate is better and the wastewater is significantly cleaner.
2. Natural dyes
This is where people get romantic about the process. Natural dyes from plants, insects, minerals; sounds beautiful, right?
In theory, yes. In practice, it's complicated.
Natural dyes have been used for thousands of years. Indigo from plants, madder root for reds, cochineal insects for vibrant pinks, turmeric for yellows. They're renewable, biodegradable, and don't require synthetic chemical production.
But here's what the natural dye advocates don't always mention:
-
Colourfastness is difficult. Natural dyes often fade significantly faster than synthetic dyes, especially with washing and sun exposure. This means garments need replacing sooner, which undermines the sustainability argument.
-
Mordants are still needed. To get natural dyes to bond properly and last, you often need mordants; aluminum salts, iron, copper. Some mordants are toxic. The process still creates chemical waste.
-
Scalability is nearly impossible. To dye fabric at commercial scale with natural dyes requires massive amounts of plant material. The land, water and energy needed to grow enough indigo or madder to replace even a fraction of synthetic dye production would be enormous.
-
Colour consistency is challenging. Natural dyes vary based on growing conditions, harvest timing, processing methods. Getting consistent colour across production batches is genuinely difficult.
I've experimented with natural dyes. They're beautiful for small-batch, artisanal work. But for a brand producing at even modest commercial scale, the practical challenges are significant.
3. Solution dyeing
This is a different approach entirely; instead of dyeing finished fabric, you add pigment to synthetic fibers while they're still in liquid polymer form, before they're extruded into fibers.
This uses dramatically less water (up to 90% less than conventional dyeing) and creates virtually no wastewater because there's no dyebath to dispose of.
The downside: it only works for synthetic fibers, and it requires committing to colours very early in production, which limits flexibility.
Some activewear brands use this for polyester. It's genuinely more sustainable for synthetic fabrics, but it doesn't help with natural fibers like cotton.
4. Waterless dyeing technologies
There are emerging technologies that use CO2 or air instead of water as the dye carrier. DyeCoo is the most well-known. They use supercritical CO2 (CO2 under specific pressure and temperature where it acts like both a gas and liquid) to dye polyester.
Zero water. No chemicals. The CO2 is recycled in a closed loop.
It's brilliant technology. The problems: extremely expensive equipment (millions of pounds to set up), only works for polyester currently and requires significant energy input to create the supercritical CO2 conditions.
I'm watching this space with interest, but it's not accessible to small brands yet.
How to actually read a clothing label
Right, so knowing all this, what can you actually do as a consumer?
Here's what to look for on labels and how to interpret it:
Organic cotton This tells you about the fiber (grown without synthetic pesticides) but says nothing about the dyeing process. Organic cotton can still be dyed with conventional, highly polluting dyes.
GOTS certified (Global Organic Textile Standard) This is better. GOTS certification covers the entire production chain, including dyeing. It requires that dyes meet specific environmental and toxicological criteria. Not perfect, but significantly better than conventional.
Oeko-Tex Standard 100 This certifies that the finished textile doesn't contain harmful substances. It's testing the end product, not regulating the production process. Still useful; it means the fabric won't leach harmful chemicals onto your skin; but it doesn't guarantee environmental sustainability in manufacturing.
Low-impact dyes Usually means fiber-reactive dyes with high fixation rates and fewer harmful auxiliaries. Good, but verify if possible because it's not a regulated term.
Natural dyes or "Botanical dyes" Sounds great, but ask about mordants used and colourfastness. If a brand is genuinely using natural dyes responsibly, they'll usually provide detail because it's complicated and expensive and they want credit for it.
Solution dyed If it's polyester or nylon, this is genuinely water-saving. Ask if the synthetic fiber itself is recycled (even better).
Bluesign certified This is a Swiss standard covering chemical management in textile production, including dyes. Very stringent. If you see this, the brand is serious about chemical safety and environmental impact.
What labels DON'T tell you:
-
Water usage in dyeing
-
Energy consumption
-
Whether wastewater was treated before discharge
-
Working conditions in the dye house
-
Whether the factory has proper chemical handling protocols
This is where brand transparency matters. If a brand can't or won't tell you where and how their fabrics are dyed, that's a red flag.
What we do at Rosenberries
I'm going to be completely transparent about our approach because I think you deserve to know exactly what you're buying.
For cotton and cotton-blend pieces: We use GOTS-certified low-impact fiber-reactive dyes. Our dyeing is done at a facility in Portugal that has a closed-loop water treatment system. Wastewater is filtered and treated before any discharge.
The dyes cost more. The facility charges premium rates because proper wastewater treatment is expensive. This adds approximately £8-12 to the cost of each garment compared to conventional dyeing.
But I can sleep at night knowing we're not contributing to river pollution in developing countries.
For our navy pieces specifically: Navy is one of the hardest colours to achieve with low environmental impact. It requires significant dye concentration to get a deep, true navy that doesn't fade to grey after a few washes.
We use a two-stage dyeing process with fiber-reactive dyes that gives us better colourfastness with less overall dye usage. It takes longer (three days instead of one) but the fixation rate is higher, meaning less waste.
What we're still working on:
I'm not going to pretend we've solved everything. There are challenges we're still navigating:
-
Colour range limitations: Low-impact dyes don't produce the same vibrant colour range as conventional dyes. Some colours (particularly bright reds and oranges) are difficult to achieve with our current dye system without compromising either environmental standards or colorfastness.
-
Cost: Sustainable dyeing genuinely costs more, and there's a limit to how much we can charge for garments before we price out the customers we want to serve.
-
Supply chain transparency: Even with our Portuguese facility, I don't have perfect visibility into every chemical used in every stage of pre-treatment and post-treatment. We're working on this, but complete transparency is hard to achieve.
The future I'm hoping for
In an ideal world, here's what sustainable dyeing would look like:
Widespread adoption of closed-loop systems where water is treated and reused, not discharged. The technology exists—it's expensive, but it exists.
Accessible waterless dyeing for natural fibers, not just synthetics. Research is happening, but it needs more funding and development.
Better natural dye technology that solves the colourfastness and scalability problems. I'd love to use plant-based dyes if they could perform comparably to synthetic low-impact dyes.
Regulatory requirements for wastewater treatment globally, not just in countries with strong environmental laws. This levels the playing field and stops the race to the bottom.
Consumer education so people understand why sustainable dyeing costs more and what they're actually paying for.
The chemistry matters
I know this got technical. But I think it's important to understand that sustainability in fashion isn't just about using organic cotton or recycled polyester.
The chemistry of how that fiber gets coloured matters enormously; for the environment, for the workers handling the chemicals, for the communities downstream from textile factories.
When you buy a navy jumper for £25 from a fast fashion brand, that price is possible partly because someone, somewhere, cut corners in the dyeing process. The cost gets externalized; paid by the river ecosystem, the garment workers' health, the communities drinking contaminated water.
When we charge £65 for a similar jumper, a significant portion of that price difference is in the dyeing alone. Proper dyes, proper facilities, proper wastewater treatment.
That's the chemistry you can't see but are paying for.
What you can do
If this resonates and you want to make better choices:
1. Ask brands about their dyeing process
Most won't have a good answer. The ones who do are usually doing something right.
2. Look for GOTS or Bluesign certification
These aren't perfect, but they're legitimate third-party verification that some level of environmental standard is being met.
3. Accept that deep, vibrant colours might not be the most sustainable choice
Natural, undyed fibers or lighter colors generally have lower environmental impact than deep, saturated colours like black and navy.
(I know, I know—our signature pieces are navy. We're working on it.)
4. Care for your clothes properly
Even the best low-impact dyes will fade if you wash in hot water, use harsh detergents, or expose garments to direct sun for extended periods. Proper care extends garment life, which is ultimately more sustainable than any dyeing process.
5. Buy less, choose better
The most sustainable dye is the one that doesn't need to be produced. If you're wearing a garment for years instead of months, the environmental cost per wear of even conventional dyeing becomes significantly lower.
The Spring collection and dye choices
Our Spring '26 collection (which launched last week—thank you to everyone who supported it) features pieces in navy, white and natural undyed cotton.
The navy pieces use the two-stage low-impact dyeing I mentioned. The white pieces are bleached using hydrogen peroxide (which breaks down to water and oxygen) rather than chlorine-based bleaches. The natural cotton pieces are undyed—just the natural cream colour of organic cotton.
These weren't aesthetic choices first—they were environmental choices that we then worked into the design.
I'm genuinely proud of the material decisions in this collection. Not perfect, but honest and thought-through.
Questions welcome
I could talk about textile chemistry for hours (ask anyone who's been stuck next to me at an industry event). If you have questions about any of this—dyeing, fabric treatment, certifications, whatever; ask them.
Reply to Friday's email, leave a comment here, send a message on Instagram. I read everything and I'll answer what I can.
The more we understand about what's actually in our clothes and how they're made, the better choices we can all make.
