Alternative silk explained

For centuries, silk came from silkworms alone. Now, biotechnology is expanding what's possible. By producing silk proteins through fermentation or genetically modifying silkworms, researchers are creating new versions of silk designed for performance and sustainability.

How silk is made

Silk comes from silkworms, which spin cocoons of fine protein fibers. These fibers are primarily fibroin, the structural protein that gives silk its strength and sheen, and are coated with sericin, a glue-like protein that holds the fibroin strands together. To harvest silk, cocoons are boiled so the fibers can be unwound intact. Thousands of silkworms are needed to produce even a single garment, and large amounts of water and energy are required to grow the mulberry leaves they feed on.

From silkworms to spider silk

For centuries, silkworms were the only known way to make silk. But in nature, spiders produce a different kind of silk with extraordinary properties: strong, lightweight, and highly elastic. Scientists studying spider webs discovered that these fibers are among the most advanced materials in biology, inspiring a new generation of bio-silks that aim to replicate or exceed these properties.

Silkworm silk vs. spider silk

While both are protein-based, silkworm and spider silk behave differently. Silkworm silk is smooth and lustrous, ideal for weaving fine fabrics, but limited in strength and stretch. Spider silk is naturally strong and highly elastic, with different types serving distinct structural and adhesive functions. Because spiders cannot be farmed at scale, biotechnology focuses on replicating these proteins through two main approaches: microbial fermentation and genetic modification of silkworms.

What alternative silk means

Alternative silk refers to silk-like fibers made without traditional sericulture (the practice of raising silkworms for silk production). Biotechnology offers two distinct approaches:

Microbial fermentation

Microorganisms like yeast or bacteria are programmed to produce silk proteins through fermentation, the same process used to make insulin or enzymes. These proteins are purified and spun into fibers that can mimic or improve upon natural silk. Often called bio-silk, this approach has the potential to eliminate the need for silkworms entirely and allow production in bioreactors at industrial scale, though significant challenges in cost and scale remain.

Transgenic silkworms

Silkworms are genetically modified to produce spider silk proteins instead of traditional silk proteins. This method combines conventional sericulture with genetic engineering, using the silkworm's natural ability to spin fibers while changing what proteins those fibers contain. The resulting material is sometimes called recombinant spider silk. Since this approach still requires raising silkworms and growing mulberry leaves, the environmental benefits compared to traditional sericulture are less clear, though it does produce fibers with spider silk performance characteristics.

Spider-inspired designs

Spider silk provides a blueprint for engineering bio-silk. In a LinkedIn post, Bolt CTO David Breslauer outlined different spider silk types and how they translate into material design:

• Dragline silk – forms the spider's framework; stronger than steel by weight
• Flagelliform silk – ultra-stretchy, acts like a bungee cord
• Aggregate silk – sticky under varied humidity, coating capture threads

These protein structures inform bio-silk design, allowing fibers to be optimized for strength, elasticity, or other properties desired by designers.

Bolt Threads (now Bolt Projects Holdings, Inc.) focuses on cosmetic and personal‑care biomaterials, though its earlier spider-silk work still informs textile innovation.

Key innovators

Several companies are pushing bio-silk toward commercialization using different production methods:

Microbial fermentation companies

These companies use engineered microorganisms to produce silk proteins, eliminating the need for silkworms or spiders:

• Spiber – Partnered with The North Face to create the Moon Parka, the first commercially available jacket made from microbially produced protein materials, released in limited quantities in 2019.
• AMSilk – Produces Biosteel® fibers used by Adidas and Omega for sustainable footwear and accessories.

Silk protein chemistry

Evolved by Nature – Converts waste silk cocoons into silk‑protein materials. Their Activated Silk™ platform is used for textile coatings and sustainable leather finishing, combining performance with eco‑friendly production.

Transgenic silkworm approach

Kraig Biocraft Laboratories – Genetically modifies silkworms to produce spider silk proteins. Their Dragon Silk™ and Monster Silk® lines insert spider silk genes directly into silkworm DNA, combining spider silk performance with established sericulture infrastructure.

These projects show bio-silk is moving from research labs into limited-edition fashion, with potential for broader adoption as production scales.

Bio-silk offers designers a new toolkit: fibers that are strong, flexible, sustainable, and tunable for specific applications.

Benefits of bio-silk

Bio-silk offers advantages for both sustainability and material performance.

Environmental and production benefits

• Microbial fermentation can reduce land and water use compared to traditional silkworm farming
• Uses renewable plant-based feedstocks instead of petroleum
• Addresses animal welfare concerns by eliminating the need to boil silkworms
• Protein-based fibers may biodegrade under the right conditions

Performance and design benefits

• Fibers can be engineered for stretch, durability, or softness
• Can be blended with other fibers for weight, drape, or texture flexibility
• Spider silk–inspired fibers can be stronger than steel by weight while remaining flexible

Barriers to scaling

Despite its promise, bio-silk faces challenges. Fermentation, purification, and fiber spinning remain costly, keeping production volumes low and prices high. Consumers and designers may be unfamiliar with bio-silk, requiring clear communication from brands. While regulatory approvals and standardization for textiles are ongoing hurdles, particularly for products involving genetically modified organisms.

The future of silk

Silk production is shifting from farms to bioreactors, though transgenic approaches show that innovation can happen within traditional sericulture as well. The technology has been demonstrated in limited commercial releases, but scaling it for everyday fashion will take time.

Like cotton, which evolved from selective breeding to modern genetic innovation, silk is entering a phase where designers can reimagine its structure through material design. This move opens up possibilities for materials that balance performance with environmental considerations.