Curious Kids: why is spider silk so easy to break when it’s supposedly stronger than steel?

Curious Kids is a series by The Conversation, which gives children of all ages the chance to have their questions about the world answered by experts. All questions are welcome: you or an adult can send them — along with your name, age and town or city where you live — to curiouskids@theconversation.com. We won’t be able to answer every question, but we’ll do our best. How is spider silk so easy to break when it’s stronger than steel? — George, aged ten, Hethersett, UK.

Thanks for the question, George — the simple answer is that spider silk breaks easily because it’s really, really, really thin. A thread in the web of a garden spider is just 0.003 millimetres across — that’s more than 20 times thinner than a hair from your head.

But there are a few more matters we need to untangle, to see how strong spider silk is, compared with steel.

Steel is a material called an alloy, which means it is a mixture of metals. The main metal in steel is iron. Other metals are added to the iron, depending on what you want the steel to do.

For example, knives and forks are made from stainless steel that doesn’t rust. To make this you’d mix iron and chromium.