Even the most sustainably sourced and made clothing can be wasteful--once you wear a shirt to the point where it's permanently pit-stained and no longer donation-worthy, it becomes waste.

Kristy Caylor and Mary Saunders looked at their own pit-stained shirts and saw a business idea. They wanted to create a clothing startup that produced no extra waste.

At Inc.'s GrowCo festival in New Orleans Wednesday, the two co-founders launched For Days, a T-shirt subscription service they say is the first fully circular fashion brand. Customers' monthly membership fees are based on the number of new shirts they wish to receive--three for $12, six for $24, or 10 for $36. But the idea is that you never really "own" the shirts; you wear them until they're worn-out and then you exchange them for new ones. The old shirts are mechanically upcycled into a new product. Customers can switch styles, colors, and sizes, essentially exchanging their wardrobe seasonally.

"I had pit-stained T-shirts, stretched out pajamas, and single socks--nobody wants to share that," said Caylor, who also serves as the CEO of For Days. "It has no residual value but there are raw materials there that are interesting."

When For Days gets a T-shirt back from a user, the garment is chopped into small pieces, mixed with water and some virgin material to extrude it into new thread. After that, a new T-shirt is made from the recycled materials and sold. The upcycling currently happens in Spain, Saunders said, but the company is working on building vertical manufacturing in its Los Angeles location to cut down on the outsourcing.

Caylor and Saunders say they aren't worried about people abusing the business model by frequently sending back T-shirts. Instead, they expect customers to rally behind the new form of consumption.

"It's very hard to change the way industries are operating right now because everything is built around the concept of produce, purchase, and pollute," Saunders said. "People want to be doing good in the world, so [we thought] how can we really align with that and get their energies towards this bigger system?"

Caylor and Saunders were building For Days in stealth mode since May of last year and closed a $2.3 million round of seed funding at the end of 2017, led by Congruent Ventures.  Saunders said the goal is for the company to expand to loungewear, socks, underwear, and even baby and children's clothing in the future.

Both Caylor and Saunders have backgrounds in fashion. The two met 15 years ago while working at Banana Republic and Caylor later hired Saunders for her first company, Maiyet, in 2010. Caylor's business sold luxury retail goods that backed a social mission. Saunders came on as the COO after she earned her degree from Harvard Business School. The two worked together at the company for years before quitting and starting For Days. 

They decided to launch the company with T-shirts--a closet staple everyone has. 

"It's one of the most iconic items of clothing," Caylor said. "It's size-, gender- and culturally-indifferent."

The co-founders had plans to launch For Days around this time, and unveiling it at GrowCo was coincidental, Saunders said. Still, she said launching to a big group of entrepreneurs has its upsides: They offer plenty of free startup advice as they window-shop.