The Nittaku Fastarc S1 is the softest and, along with the Fastarc P1, the fastest rubber in the series. It features a slightly softer sponge with a hardness of 44° and a top sheet with widely spaced pimples, providing a powerful catapult effect. The combination of the softer surface and sponge produces a flatter trajectory and high momentum. While the rubber’s strong compression can make it more challenging to control during fast rallies, it offers excellent feel and precision on gently executed topspin shots.