DONIC BLUESTORM - A storm brews ! A comprehensively thinner top surface rubber, subjected to high tension, allows space for a thicker sponge - generating extra power and speed. The DONIC Bluestorm Series offers noticeably greater acceleration whilst retaining its outstanding spin and speed characteristics, making the latest trend. Z1 with its medium pored sponge and a short, wide pimple structure is the hardest and fastest of the three Bluestorm versions.