In 1992 a Cairo surgeon found a male contraceptive that worked on every man who wore it, and it was a scrap of polyester. Ahmed Shafik ran the department of surgery at Cairo University. He took 14 healthy men and fitted each with a polyester sling to hold the testicles, worn day and night for a year and changed only when it needed a wash. Between four and five months in, all 14 had no sperm at all. Zero. They stayed at zero for the rest of the year. He took the slings off and waited. The counts came back, on average, about five months later. A biopsy at six months had shown the tubes that make sperm degenerating, and the damage was still visible half a year after the polyester came off. He had already tried it on rats. In 1993 he dressed 75 of them in tiny trousers of cotton, wool, polyester or a polyester blend and left them in them for up to a year. The rats in polyester mated noticeably less often. The rats in wool carried on as rats do. He tried dogs next. A dozen in polyester pants, a dozen in cotton, for two years. The cotton dogs were unchanged. The polyester dogs' counts fell, their abnormal sperm rose, and two of them still had not recovered a year later. He measured the static the fabric built up as it rubbed against skin, and blamed that. Cotton built up none. He published all of it, called the sling a safe and reversible method of contraception, and in 2016 was given an Ig Nobel Prize, the award for research that makes people laugh first and think afterwards. Between 1973 and 2018, sperm counts across the world fell by more than half. Over the same years polyester went from a novelty to the most worn fibre on earth, 59% of everything spun in 2024, and now standard in sports underwear, gym shorts, bedsheets and the school uniform. A surgeon put fourteen men in it and switched their fertility off like a tap. The rest of us are still wearing the trial.