Bowling balls were made of lignum vitae (hardwood) until the 1905 introduction of rubber balls. Polyester ("plastic") balls were introduced in 1959 and, despite developing less hook-generating lane friction than rubber balls, by the 1970s plastic dominated over rubber balls which then became obsolete with the early-1980s development of polyurethane ("urethane") balls. Urethane balls developed more friction with the newly-developed polyurethane lane finishes of the day, sparking the evolution of coverstock technology to pursue ever-stronger hooks with correspondingly higher entry angles.