Nike Free (flexy sole like the 3.0 but with about 4mm more cushioning throughout). This is perfect for runners who are new to the "Free" series. Anything with the suffix "TR" in the model name is intended for cross training. This isn't always apparent. A Nike Free Walk walking shoe is also available. The Nike Free Xilla is a sneaker designed for cross-training. Nike Free shoes are intended to represent points on a spectrum spanning supported but uncorrected jogging to unsupported barefoot running (on a theoretical spectrum of 10.0 for most support to 0.0 for least support, actual shoes produced have ranged from 7.0 to 1.0).