To facilitate the rock-climbing experience he developed - in the 1930s - the first rubber-soled, soft shoes specifically engineered for serious rock work. He wore these on the sandstone boulders as well as on the granite walls of the Alps, where he made several famous first ascents, including the north face of the Aiguille du Dru. These shoes, known as PAs, became the model for future generations of climbing footwear. Indeed, the version available in the 1950s looked remarkably like modern climbing footwear.