Each year, more than 500,000 spectators line the streets of Boston on the third Monday in April to witness one of the true classic long-distance running events. That’s when the Boston Marathon takes place, sending more than 35,000 runners on a 26.2-mile jaunt across Beantown. This year, one of those runners will be wearing a unique pair of running shoes that will no doubt help him to stand out from the crowd.

Footwear engineer Chris Bellamy will take to the streets of Boston on April 16 wearing a pair of flip-flops that he says are as comfortable and supportive as just about any athletic shoe. The flip-flops are made by a company called Wiivv (pronounced “weave”), which is preparing to release a full line of custom-built sandals later this spring. But, these sandals promise to be completely different from anything else on the market today, whether you plan to run a marathon in them or not.

The shoe company’s ambitious strategy is to customize its sandals specifically for each individual. To do that, it will 3D-print its footwear to the exact needs of its buyers. The process begins when customers visit the Wiivv website and select the style of sandal they want. Next, they take precise measurements of their feet via a specially designed app that is available for iOS and Android. Those measurements are then transmitted directly to Wiivv, which prints the shoes and ships them directly to the customer in about ten days. If this all sounds a little too good to be true, keep in mind that the company is already doing just that with its line of custom insoles.

Wiivv’s app measures more than 200 points on an individual’s foot to ensure that it gets the perfect contour map. The software takes into account foot length, width, and volume, as well as toe spacing, when creating the custom shoes. When the sandals eventually 3D-printed, the system selects the proper size of the arch, the contour of the heal, and even the exact placement of the thong between the toes. In short, they promise to be the best fitting flip-flops customers have ever seen or Wiivv will give them their money back.

Creating custom-made, 3D-printed sandals is one thing, but wearing them in the Boston Marathon is an entirely different kind of challenge. Bellamy says that Wiivv is focused on creating the most comfortable and supportive flip-flop possible, and while the shoes aren’t meant for running long distances, he thinks this is a good way to demonstrate just how good they truly are.

“We spent many sleepless nights driving fairly radical innovations in design and materials, and optimizing for biomechanics and comfort. So I am not worried at all about going the full 26.2 miles,” Bellamy says in a press release announcing his Boston Marathon run. “We’ve reengineered every part of the traditional flip-flop to design the most comfortable, optimized sandal ever created, and I’ve had this marathon in the back of my mind through every decision we made,” he added.

Will his feet hold up? We’ll just have wait until next Monday to find out.