BlackCode is the softest polyester string on the market today, and features a pentagonal cross section for optimal spin. BlackCode is Tecnifibre’s best selling polyester and is our most recommended polyester string. Most players do not require the stiffness offered by the other polyesters in the Tecnifibre range, and a softer string will help avoid injury and cause less fatigue during play. If you find BlackCode too soft in terms of feel, then try RazorCode. All Tecnifibre polyester strings use Thermocore technology, a heating and cooling process during the production phase to provide added flexibility to polyester strings for added comfort. Through this technology, Tecnifibre make the softest polyester strings on the market.