What If Denim Could Be Made With Spider Silk And Orange Peel?

Inside Pure Denim, a 22-person Italian mill exploring how far denim can stretch.

I recently had the absolute pleasure of interviewing Pure Denim’s owner, Luigi Caccia. I left thinking about how much a small team can take on when it is willing to follow ambitious ideas all the way through production.

Founded in 1974, Pure Denim is one of Italy’s earliest denim mills. Its size gives the team room to experiment closely with fibres, technologies and processes that larger operations may struggle to introduce.

I wanted to share some of what they are working on because it deserves far more attention than it deserves.

How far can denim stretch as a material?

Pure Denim works with silk, cashmere, wool and other noble fibres alongside cotton. These materials give the team a way to explore how denim might feel and behave differently while still retaining its familiar construction.

In some projects, the mill has used up to 40 percent cashmere for specific clients. The team is now curious about whether a 100 percent cashmere denim could eventually be possible.

Their work raises interesting questions about luxury. For Pure Denim, it seems to begin with exceptional materials and the knowledge required to handle them well.

Bringing Sea Island cotton into denim

Another fibre they work with is Sea Island cotton grown in Barbados. Until recently, it was used primarily by luxury shirt makers. Its value comes from the rarity and quality of the fibre, rather than a large certification story.

Pure Denim is now growing Sea Island cotton hydroponically in Europe and exploring its use in denim. Working with a fibre like this requires care throughout the process and its value can easily be lost if it is treated as an interchangeable input.

Spider silk without the spider

This is where things became very fascinating.

Pure Denim has been working with AMSilk, a German biotechnology company founded in 2008 that produces silk proteins inspired by spider silk at an industrial scale.

The process uses microorganisms and fermentation to produce protein. Certain bacteria are fed a sugar-rich solution, after which the resulting protein can be dried into powder and extruded into filament.

The material carries many qualities associated with natural silk, including breathability, antibacterial properties and thermoregulation.

Pure Denim began working with AMSilk around a year ago and first presented the development at a trade fair in November. A luxury brand is already using AMSilk for part of its silk content, bringing the material beyond the laboratory and into commercial products.

For Pure Denim, the fibre can be introduced into systems the mill already understands. It can move through familiar warp preparation, weaving and fabric construction processes so it doesn’t disrupt production lines too drastically.

The material remains expensive, which will affect how quickly it can reach wider use. Still, seeing it move through an existing denim system makes the possibility feel tangible.

Could microorganisms produce indigo too?

Pure Denim has also been experimenting with bio-based indigo through projects involving SonoVia and Colorifix, a European company using biosynthesis to recreate the properties of plant-derived indigo.

As with AMSilk, microorganisms are used to produce something that has historically come from petrochemicals or from natural sources that can be difficult to grow at scale.

Pure Denim now hopes to run an industrial trial. The team is willing to test how the technology behaves inside an operating mill, where new ideas meet the realities of machinery, consistency and production volumes.

The plastic used before denim is woven

Before we reach the orange peel, there is another part of denim production worth understanding.

Cotton yarns are usually coated with a sizing agent before weaving. This protective film helps them withstand the mechanical stress of the loom.

Polyvinyl alcohol, also known as PVA, is a common option because it is inexpensive and effective. According to Pure Denim, it also contributes to the particularly stiff handle associated with some Japanese denim. During processing, the sizing is washed out and can enter the water system.

Pure Denim has chosen not to use PVA.

Working with the University of Siena, the mill developed NaturalReco, a sizing agent made using pectin from the white pith inside orange peels. The pectin is modified so that it can perform effectively on cotton yarns.

NaturalReco performs the same protective role while finding a new use for an existing food waste stream. Pure Denim decided against patenting it, allowing other mills to introduce the technology into their own processes.

That decision stayed with me, as the team believes the solution will have more value if it can spread through the industry.

Other alternatives are now emerging, including sizing agents made with pea protein and other plant-based binders. Pure Denim helped show what could be possible.

Rethinking stretch denim

I learned more about Pure Denim’s approach to stretch when I met Luigi again at PV Denim in Milan, where the mill was presenting a project with a material lab.

Pure Denim works with XLANCE, an Italian elastic yarn produced differently from conventional spandex.

Traditional elastane is commonly made through a dry-spinning process involving solvents. It also requires heat setting at temperatures of approximately 180 to 190 degrees Celsius. This process locks the stretch into the fabric and can contribute to the slightly stiff, synthetic handle often associated with stretch denim.

XLANCE is melt-spun without solvents and does not require thermofixing at the temperatures used for conventional spandex. This helps the finished denim retain a more natural feel. According to the company, its production also uses around 40 percent less energy than conventional elastane production.

XLANCE is now developing a bio-circular version of the fibre made from used cooking oil collected from food processing and industrial kitchens. This could replace some fossil-based inputs while making use of an existing waste stream. Pure Denim is following the development closely.

The fibres Pure Denim chooses to avoid

Pure Denim has clear material boundaries. The mill does not use polyester, viscose or Tencel. Elastane is used in small quantities when stretch is technically required.

If a client requests a fabric that falls outside those boundaries, the team will direct them elsewhere.

The word “sustainable” has become so diluted that claims often require extensive documentation before they carry much meaning. Pure Denim’s boundaries make its position easy to understand.

Its approach to wool and cashmere is equally specific. For recycled wool, the team looks for GRS certification and Italian provenance. When working with merino, it speaks openly about the complexity of supply chains extending through Australia, South America and South Africa.

The mill also uses carded wool, including fibres with small imperfections that can bring texture and depth to a fabric.

Another material in its archive is FoxFibre cotton, developed by Sally Fox. The cotton grows naturally in shades of brown and green, reducing the need to add colour through dyeing.

Has certification become the end of the conversation?

One line from my notes has stuck with me.

“Sustainability has unfortunately stopped at certification.”

It was offered as a fairly plain observation about where the industry has landed.

Certification can offer valuable standards and accountability. It can also create a sense that the presence of a label has answered every relevant question.

Much of Pure Denim’s work begins before an established certification is available. In other cases, certification may be too expensive or rigid for a small experimental project.

Sea Island cotton has little certification attached to its story. AMSilk remains expensive and available in low volumes. NaturalReco was shared without protected intellectual property. These examples sit awkwardly within frameworks designed around more established materials and processes.

Looking at them requires another form of assessment. We have to examine where the material comes from, how it was produced and what happens when it meets an industrial system.

What happens after the sample stage?

Most clients still purchase standard products in much larger volumes. Pure Denim’s experimental materials receive considerable interest during sampling, but that curiosity does not always become an order.

Brands may want to learn about a new fibre or remain close to its development while continuing to buy familiar materials at familiar prices. Current economies of scale keep rewarding options that are cheaper and easier to certify.

Experimental materials need clients who understand what they are supporting and are willing to pay for the work involved. More of those clients are appearing, although progress remains uneven.

Meanwhile, this 22-person mill is testing fibres made through fermentation, replacing plastic sizing with pectin from orange peels and seeing how materials once reserved for luxury shirts might behave as denim.

I am very glad places like Pure Denim are willing to keep asking these questions :)

Further reading:

• AMSilk — biotech silk protein innovation

• Pure Denim