The fashion industry have been doing the same thing for decades. By hanging below the torso, testicles stay cooler — by about 4 to 6 degrees, typically — than the rest of the body. That helps them make happy, functional sperm cells. https://www.npr.org/sections/health-shots/2018/08/08/636901101/boxers-or-briefs-experts-disagree-over-tight-underwears-effect-on-male-fertility