Spider Silk: Stronger Than Steel — Bolt Threads / Spiber / Utah State University

Biological model: Golden silk orb-weaver spider (Nephila clavipes)

Company: Bolt Threads / Spiber / Utah State University

Spider silk is five times stronger than steel by weight, more elastic than nylon, and biodegradable — yet spiders have never been farmed like silkworms. Bolt Threads and other companies have now synthesised spider silk proteins using yeast fermentation to create the world's highest-performance natural material.

The challenge

Synthetic high-performance materials like Kevlar require toxic solvents, high temperatures, and are not biodegradable, while no synthetic matches spider silk's combination of strength, elasticity, and toughness.

Nature's strategy

Golden silk orb-weaver spider (Nephila clavipes)

What was emulated

Dragline silk production: self-assembling protein structures create fibres with ~1.3 GPa tensile strength, 40% elongation, and toughness exceeding Kevlar.

The innovation

Recombinant spider silk proteins produced via yeast fermentation and wet-spun into fibres, replicating nature's strongest material at industrial scale.

Full case study

Dragline spider silk — the type used for the outer frame and radial threads of a spider's web — has mechanical properties that no synthetic material has yet matched simultaneously. It has a tensile strength comparable to high-grade steel (about 1.3 GPa), an elongation at break of up to 40% (far more elastic than steel), and a toughness (energy absorbed before fracture) that exceeds Kevlar. Unlike steel or Kevlar, spider silk is also biodegradable, produced at room temperature in water, requires no toxic solvents, and can be recycled by the spider. A web the thickness of a thumb could theoretically stop a Boeing 747 in flight. Spiders cannot be farmed (they are territorial and cannibalistic), so researchers have pursued two routes: transgenic silkworms that produce spider silk proteins (Utah State University), and fermentation-based synthesis. Bolt Threads cultures genetically modified yeast that produce recombinant spider silk proteins, which are then spun into fibres using wet spinning. Their "Microsilk" fabric has been used in limited commercial products. Applications under development include: ballistic armour lighter and more flexible than Kevlar, surgical sutures that are stronger and more biocompatible than current materials, aerospace composites, and high-performance sportswear.