Thursday, 7 July 2011

The Levi Strauss effect

One way of explaining the thermal bridge effect is retelling a story from the history of fashion. This story comes many years after Levi Strauss started using a fabric of Nimes (in France) for trousers in the style of Genoa. To increase the strength of these denim jeans, he put copper rivets in strategic places. In the early garments, one of these rivets came where four bits of cloth meet at the crotch. At least until one day in 1933 when Levi Strauss president, Walter Haas Sr. was out camping, wearing a pair of 501s, and he sat down by a campfire. He hadn't looked very carefully, and on the seat was an iron that had just been in the fire. 

I'm sure you can imagine the effect of the hot iron on the rivet, the speed of the heat transfer, and the part of Mr Haas's body to which said heat was transferred. Needless to say, the crotch rivet was removed from the design.

This is a good example of a conflict between structural considerations and thermal considerations. In fact, the truth is a little less colourful, and although Levi Strauss used this story in an advertising campaign, the main reason for removing the crotch rivet was rationing of copper during the second world war, and economics played its hand.