Yonex Poly Tour Air is a co-polymer monofilament with an elastic HR polymer additive. The result is a spin-friendly control string with impressive shock-absorption. In fact, this is not only the softest poly-based string we’ve tested by Yonex, but it is also one of the softest polys we’ve ever tested in our Tennis Warehouse University String Lab. In addition to being an obvious choice for players looking to transition into the polyester universe, POLYTOUR AIR is perfect for the polyester veteran who wants a more tendon-friendly ride.