What were footballs made of in 1914 to 1918?

During the years 1914 to 1918, footballs were primarily made of leather. The outer casing was typically made from cowhide or other animal hides, which were stitched together to form a spherical shape. Inside, the balls were inflated with a bladder, often made from rubber or gut, to provide the necessary shape and bounce. The materials were durable for the time, though they required regular maintenance to keep them in good playing condition.