Head Gravity is a hybrid tennis string featuring an unlikely combination of two co-polyester monofilaments. The main strings feature sharp edges for digging into the ball and the cross strings are thin, round and slippery (so as to facilitate the "snap back" of the mains). The result, according to our playtest team, was vicious ball rotation -- a.k.a. spin. Another prominent feature of Gravity was its crisp feel, which also managed to be surprisingly arm-friendly for a full poly setup. This hybrid also proved quite lively, which resulted in control problems for one of our playtesters -- a problem that was aggravated by tension loss (the primary downside of soft co-polys). Although neither playtester is planning on switching to Gravity, they agreed that this hybrid is a great option for players who want a comfortable entry point into the universe of polyester. Gravity should also work well for any poly veteran who wants a spin-friendly option that doesn't overtax the tendons.