Spider silk is stronger than steel of the same weight

The silk strand a spider trails behind itself — its dragline, the lifeline it dangles from and the scaffold of its web — is one of the most remarkable materials in nature. Weight for weight, it is stronger than steel.

The comparison only works on a fair footing. Steel is dense, so a steel cable of a given weight is far thinner than you’d guess — and a dragline strand of that same mass can carry a comparable or greater load before snapping. Researchers peg dragline silk’s tensile strength in the range of high-grade steel, around 1 to 1.7 gigapascals, while the silk is roughly a sixth of steel’s density. Match the weight and the silk comes out ahead.

What truly sets silk apart isn’t raw strength but toughness — the total energy a material soaks up before it breaks. Silk can stretch a long way before failing, sometimes well over a third of its length, so it absorbs enormous amounts of energy, outclassing steel and rivaling the best engineered fibers like Kevlar. That blend of strength and stretch is exactly what lets a fragile-looking web stop a flying insect dead without tearing apart.

A dragline strand is several times stronger than steel, on a weight-for-weight basis.

The toughest known belongs to Darwin’s bark spider of Madagascar, whose silk measures around 350 megajoules per cubic meter — tougher than any other biological material yet recorded. A spider achieves all this at body temperature, from a watery protein squeezed through a gland, with no furnace and no factory. Materials scientists have spent decades trying to copy the recipe, and nature still has the edge.