Gregg Wallace visits two factories in Italy and Wales to explore the fascinating secrets behind how Welsh jeans brand Hiut make their trousers, learning how denim cloth is made and then transformed into one of the world's most popular items of clothing.Meanwhile, Cherry Healey visits a zip factory to learn how the ubiquitous fastener is made, and she heads to the research and development facility of a denim manufacturer to witness environmentally friendly ways of distressing denim to make a new pair of jeans look old.Historian Ruth Goodman discovers an unknown name in the history of jeans who helped to shape their design forever, and uncovers the fascinating history of indigo dye.