Danielle Elsener’s work to promote zero-waste fashion is gaining the attention of apparel makers, potentially revolutionizing one of the most wasteful and polluting sectors in existence.

“I never ask people, just casually, for their phone number,” Evan (Will Brill) says. This is how he greets Renesha (Brittany S. Hall), a woman he met in a bar some time before, whose number he’d asked ...