For decades, humble denim jeans have been at the heart of our wardrobes. Durable, comfortable, and always in fashion, denim is an evergreen fabric. But, unbeknownst to many, the vibrant hues of blue or indigo come at a high environmental cost. Traditional dyeing processes, which give denim its characteristic color, rely on methods that are not only antiquated but starkly unsustainable. But there may be a better way to do things — and a new study describes how.

The dark side of denim

Denim dyeing is a $80 billion industry and it’s not a very sustainable one. Conventional dyeing relies heavily on harsh chemicals which can pollute waterways if not properly treated. Even if they are properly treated, the UN estimates that it takes 3,781 liters of water to make one pair of jeans. The process also generates a lot of CO₂ and denim is the largest contributor to microfiber pollution. While there’s been a lot of progress in sustainable dyeing, there’s still a long way to go.

The production of blue denim currently uses a dye called indigo — the only known molecule that can provide the unique colour of blue denim. Most indigo dye produced today is synthetic, and we make around 80,000 tons of it each year. Before indigo is obtained, indican — a colorless, organic, water-soluble derivative — is produced. Ditte Welner, Katrine Qvortrup, and colleagues from Technical University of Denmark describe the most sustainable ways to obtain this indican.

While the study did not find new methods, it provides a comprehensive review of existing methods, comparing their cost, effectiveness, and sustainability.

Greener denim

They start with something called indoxyl glycosyltransferase. This chemical, found in the indigo-producing plant Polygonum tinctorium, is capable of economically producing indican on an industrial scale. Already, this is a promising discovery, but this is where it gets interesting.

With the indican produced this way, they also managed to demonstrate a sustainable dyeing process that converts the indican to indigo dye. They used two variants: one with enzymes and another with light. In the light driven approach, they showed that various light sources help the indigo stick to the fabric better. They tested LEDs, natural light, and even a household light bulb.

Lasers also show promise when it comes to dyeing denim without light.

“Lasers have high potential in the denim industry to bring a lot more sustainable value to the clothing and fashion industry by moving this approach for development of laser systems,” the researchers write in the study. The process is environmentally responsible and cost-effective, the researchers add.

Cheaper and better for the environment

Both approaches drastically reduce denim’s environmental impact. Light-driven dyeing reduces the overall environmental impact by 73% and the enzyme dyeing was even better: 92%. Considering that around 4 billion pairs of jeans are traded per year, these methods could reduce yearly emissions by 3,500,000 tons. That’s the equivalent of taking around 1 million cars off the road.

Implementing this sustainable dyeing technology on a global scale has the potential to transform the denim industry. It can satisify the increasing consumer demand for environmentally friendly products and could lead to wider adoption of sustainable practices in fashion manufacturing — expanding it to more than denim. Moreover, this innovation could enhance the well-being of workers in dyeing mills by minimizing exposure to toxic substances and reduce toxic waste.

The researchers say that minimizing environmental harm will also improve both the transparency of the supply chain and the overall sustainability of the textile industry.

“The modern denim industry is one of the biggest contributors to the textile-based global economy and essential to the economic and social growth of many developing countries. The industry of denim is expanding at a faster rate as a result of several factors, including urbanization, the westernization of lifestyles, rising fashion consciousness, and an increase in the desire for a more casual appearance. Unfortunately, the method of manufacturing denim has a negative impact on the environment due to the release of colored effluent, heavy metals, acids, alkalis, enzymes, and other pollutants. This review provides an overview of various environmentally friendly chemical processing techniques to produce sustainable denim,” the researchers conclude

The study was published in Nature Communications.