To find out, the team fired beams of ionised metal compounds at lengths of silk from the orb-weaving spider Araneus diatematus using a technology called atomic layer deposition (ALD). As well as coating each silk fibre in a fine metal oxide, some metal ions penetrated the fibre.They tried zinc, aluminium and titanium compounds, all of which improved the mechanical properties of the silk. "With all three metals, the fibres can hold three to four times as much weight," says Knez. The fibres also become stretchier, so that their toughness - the energy needed to break a strand - rises even more. "The work needed to break the fibre rises tenfold with titanium, ninefold with aluminium and fivefold with zinc," he says. The results are published in the journal Science (DOI: 10.1126/science.1168162).