Did you know that just 1km of three-lane motorway costs £13 million to build? But what are our roads made of and what makes them so strong? Our intrepid pair tests the durability of asphalt using a flame thrower, a high pressure water jet and finally, some petrol. Afterwards, we get walking at a boot factory where remote-controlled mechanical feet test water-proof capabilities and a real human endures temperatures of -40C, all in the name of testing. Then Richard delves into the history of the telephone while Jonny takes his angle grinder to a catalytic converter to see what’s inside.