Three years ago David Hall's life was turned upside down. The engineering student's sister was hit by a car when riding her bike in Philadelphia. While his sister lay in a coma, Hall and his family were asked the same question over and over again: "Was she wearing a helmet?"

She wasn't.

This led Hall and his classmate Jordan Klein to ask, "Why wasn't she wearing a helmet?"

Hall's sister, who simply preferred going helmet-free, eventually recovered from her injuries, but Hall and Klein continued to research why most cyclists do not wear helmets. In 2012 a study by Heidelberg University estimated that 29% of American adult cyclists always wear one, while 15% occasionally do. New York City does not require cyclists to wear them.

"Seeing the consequences firsthand and then seeing how big of a problem it was in the U.S., Jordan and I kind of looked at each other and said, 'We have to do something about this,'" Hall said.

They came up with a helmet that is collapsible and fashionable. The pair produced it in 2015 and took the top prize in the Red Bull Launch Institute, a competition for entrepreneurs.

Their Brooklyn-based startup, named Park and Diamond for the Philadelphia intersection where the crash occurred, is launching the helmet on Indiegogo, where it already has surpassed its crowdfunding goal of $50,000 and raised more than $450,000 since mid-September.