Fit
Flyknit uppers are remarkable in that they have virtually no structure to them, yet they keep the foot wrapped securely. The single-seam Flyknit material has stretch capability to accommodate various foot shapes, and the soft Flywire bands give it strength and keep it anchored to the midsole platform. The lacing system of the Free RN Flyknit distributes tension very evenly and effectively through the midfoot, and our testers experienced no slipping or movement inside the shoe during our testing. The rearfoot stays secure in the heel cup, while the last is rounded in front to accommodate full toe splay. 

Comfort
It’s hard to imagine a softer or more comfortable upper than the Free RN Flyknit construction, which feels like a slipper that is highly ventilated to cool efficiently and dry quickly. There’s no padding anywhere in the upper, which is a testament to how effectively the soft uppers move without the foot and avoid chafing. The only potential drawback is low toe clearance in the forefoot if you like space to wiggle your toes vertically. Underfoot comfort is excellent thanks to the improved cushioning properties of the midsole. 

Responsiveness
Nike revamped its midsole foam for the Free RN Flyknit, introducing a technology Auxetic Tri-Star geometry. The material is designed to mimic the foot’s natural motion of expanding laterally on impact before recoiling at lift off. The new midsole foam becomes thicker in the perpendicular direction when impact forces strike it vertically. The result is a combination of soft cushioning plus a strong rebound effect to propel the foot off the ground. The upwardly curved toe region provides some extra spring at toe-off, and our testers noted a consistently smooth push off.

Ride Quality
The midsole unit of the Free RN Flyknit is divided into diagonal and sagittal (heel to toe) units that are divided by deep flexion grooves; this enhances the midsole foam’s ability to expand and retract in specific regions for a more natural foot movement. The downside of these grooves is that small rocks get lodged in them very easily, and inevitably you’ll encounter one ill-placed stone that causes you to alter your stride or pause to remove it. There is virtually no outsole rubber except for a few dime-sized spots at the back of the heel and the tip of the toes, so traction is lacking on loose gravel (where you’ll have significant rock problems anyway) or wet road surfaces. 

Speed: 
With impressive cushioning, secure fit, and excellent midsole energy transfer, the Nike Free RN Flyknit makes it easy to generate fast leg turnover for speed training or race day. However, the poor traction makes the curves of a track a little sketchy, and the flex grooves may catch rocks on the roads, so you’ll need to pick your locations wisely.