Originally engineered in 2004 by Tobie Hatfield and Eric Avar, the Nike Free Run broke the constraints of what a traditional running shoe was supposed to look or feel like. Inspired by Stanford athletes that were found training barefoot on a field, the designers decided to celebrate minimalism to offer runners a more natural feel. The series has a numbering system that represented the amount of cushioning in each model. The Nike 3.0 Free is the lightest and lowest and the Nike 7.0 Free has the most cushion and support. The Nike 4.0 Free and Nike 5.0 Free is a nice compromise of lightweight comfort and supreme flexibility. Today, Nike Frees are worn casually just as much as they are worn for working out, thanks to their lightweight, flexible design and sleek aesthetic. Now offered in a wide range of materials like Flyknit and with boosted technology included Nike Flywire, the latest Nike free run shoes represent the marriage between modern design and the original spirit of minimalism that Free Run was built on.