Gregg Wallace explores the HSL factory in West Yorkshire to find out how they make more than 5,000 sofas every year. The huge site has 250 staff dedicated to furniture making. Gregg is following the production of one of their best-selling sofas, the Burros Classic in indigo.Cherry Healey learns about the science of light bulbs to create the perfect environment to snuggle up on the sofa and visits a foam factory to see how comfy padding is produced in just a few minutes.Historian Ruth Goodman takes a front row seat to discover the history of the sofa and stitches together the fascinating story of one of the world's most famous sewing machines.