Beginning around 1960 Bob Lange experimented with ways to replace leather with plastic. Early examples used a lace-up design, but in 1964 he combined a new, more flexible polyurethane plastic with the overlapping flap and buckle system from Henke to produce the first recognizably modern ski boot. Production examples appeared in 1966, and when Nancy Greene started winning races on them, the plastic boot became a must-have item. Replacing leather with plastic dramatically improved stiffness and control, along with durability and warmth (leather boots had a way of soaking through, which led to wet, frozen feet). Over time the cuff around the leg evolved upward, starting just over the ankle like leather boots, but rising to a point about half way to the knee by the 1980s. Only minor changes have occurred to this basic design since then.