"What is the strongest substance in the universe? Some people say it is spiderweb, because it is stronger than steel. Is it iron? Is it flint? Is it diamond because diamond can be only be cut by diamond?" asks Françoise Michel. Adam and Hannah put a variety of materials, from biscuits to spider web, under the hammer to test their strength. In their quest to find the strongest substance they quiz materials scientist Mark Miodownik, engineer Danielle George and spidergoat creator, Dr Randy Lewis from Utah. Features archive from 'Horizon: Playing God', first broadcast in January 2012. Please send your Curious Cases for the team to investigate to email@example.com Presenters: Adam Rutherford, Hannah Fry Producer: Michelle Martin.