The Dynafit ZZero 4U-TF Alpine Touring Ski Boots take Dynafit s best-selling ZZero boots and add extra downhill prowess thanks to a PU shell. If you want Dynafit s legendary best-of-both-worlds formula, the ZZero 4U-TF boots offer unrestricted, lightweight climbing, and a redesigned shell and liner specially built for female skiers. Polyurethane construction adds strength and durability, making the ZZero 4U-TF Dynafit s most downhill-oriented boot.