Is Spider Silk Really Stronger Than Steel?

Spider silk doesn’t look particularly impressive. It’s thinner than a human hair, light enough to drift on the breeze, and fragile enough to disappear in a single swipe of a broom. 

Yet pound for pound, some spider silks are stronger than steel and tougher than Kevlar — the material used in bulletproof vests. So how can something so delicate outperform some of the toughest materials humans have ever invented?

Small Thread, Big Performance

First, comparing spider silk to steel and Kevlar needs a little unpacking (unspooling?). A steel wire of the same thickness is generally stronger than spider silk in absolute terms. What makes spider silk remarkable is that it’s incredibly strong for its weight while also being unusually stretchy. 

Similarly, Kevlar can withstand greater pulling forces than spider silk before breaking, but spider silk stretches even farther before it snaps. Spider silks can stretch anywhere from 30-200% of its size, depending on the type. This rare combination of strength and flexibility is known as toughness (yep, that really is the scientific term for it) and allows it to absorb enormous amounts of energy before breaking. 

The secret to this lies in the chemical composition and physical structure of the silk. Spider silk begins as a liquid made almost entirely of proteins called spidroins. As the liquid is pulled through the spider’s spinnerets, the proteins line up and harden into a fiber. 

At the microscopic level, the fiber is built from tiny, tightly packed crystalline regions that provide strength, connected by softer, elastic regions that let the silk stretch. Think of it as a natural composite material that combines rigid reinforcements with flexible springs.

Not all spider silk is the same. Most spiders spin several different kinds, each specialized for a particular task. Dragline silk — used as a lifeline and to form the framework of a web — is among the strongest natural fibers in the world. 

Sticky capture silk is much stretchier, keeping it from snapping as it absorbs the impact of a flying insect (or your face when you unwittingly walk into one). Other silks are used to wrap prey, protect eggs, or build shelters.

These remarkable properties have made spider silk a favorite of materials scientists, who look to use synthetic versions in everything from surgical sutures and artificial ligaments to biodegradable textiles and lightweight protective gear. 

Reproducing natural spider silk, however, has proven difficult — not least because many spiders are territorial, cannibalistic, and decidedly uninterested in being farmed.