The Times Square New Year's Eve ball introduced in 1955 was made of aluminum.
More precisely, the aluminum ball debuted for the 1955–56 celebration and was the third ball in the tradition's history. It replaced a 400-pound iron ball that had been used since 1920, reducing the new ball's weight to about 150 pounds.
The lightweight design took the form of an aluminum cage and measured 6 feet in diameter. Its construction reflects the practical evolution of the display: the ball had to be large and visible while remaining manageable for the rigging and lowering equipment atop One Times Square.
The wording often causes a numbering mix-up. The 1955 ball is sometimes casually called the “second” modern ball because it replaced the iron version, but historical accounts generally count the original 1907 ball, the 1920 iron ball, and the 1955 aluminum ball as the first three. The aluminum design remained in service, with modifications, for decades.