Apparel retailer Gap (GPS -1.28%) announced on Thursday it would be partnering with used clothing reseller thredUp. Consumers can retrieve their delivery bags and labels from participating Gap stores, and will receive store credit when they send their secondhand garments to thredUp for resale.

Photograph of woman shopping in used, secondhand clothing store.

Image Source: Getty Images.

Secondhand clothing, once well outside of mainstream retailing's usual fare, is now becoming commonplace within the industry. Department store chains JC Penney and Macy's  both now maintain thredUp shops in select stores, selling merchandise supplied by thredUp. Nordstrom, meanwhile, has established a secondhand clothing venue called See You Tomorrow that operates online with one brick and mortar locale in New York.

The partnerships reflect the convergence of two trends, one of which is consumer efforts to get more from their wardrobe budgets. The other is greater interest protecting the environment. The U.S. Environmental Protection Agency estimates that only 15% of textiles were recycled in 2017, with more than 11 million tons of textiles ending up in the nation's landfill last year.

Used clothing, however, isn't just a public service. It's also big business, with thredUp suggesting this sliver of the apparel market alone was worth $28 billion in 2019. The company expects to it to grow to more than a $50 million market by 2023.

ThredUp has similarly partnered with other consumer-facing companies, but Gap will be its biggest partner yet when its so-called Clean Out bags and labels are available at stores beginning in April.