“Sustainability” was the buzziest buzzword in the air during last week’s edition of Pitti Uomo, the world’s largest men’s fashion trade show, in Florence, Italy. As I navigated countless rows of designers’ booths, those pitching the clothes hurled the word at me again and again in reference to pieces that otherwise had no similarity. At Woolrich, the 189-year-old Italian-based outerwear brand, it was applied to the development of hood linings made of corn, in faux-fur form. At Far Afield, a British outfit, the word described a jolly pair of citrus-patterned swim trunks constructed from recycled water bottles. The word...