Modern golf balls employ novel materials such as polymers, silicone, and synthetic rubber to improve aerodynamics and achieve higher distance-to-spin ratios. The modern ball is not wound with yarn like the old ball, but instead is molded from a single piece of hard plastic or clay. The fillers in the ball serve to reduce the weight of the ball and provide better control during play. The earliest golf balls were made out of feathers stuffed into animal skins with any material suitable to maintain the shape of the ball. These early balls were often painted black for improved visibility. In 1703, George Hamilton invented the first rubber ball, which was covered in leather. In 1887, John Moyer created the first steel ball, which was coated in silk cloth and contained 65 grams (2.5 oz) of steel. Modern golf balls can be divided into two categories: solid and liquid-filled. Solid balls are composed of one primary material, such as polybutadiene or ethylene acid copolymer, while liquid-filled balls contain multiple materials in internal layers that expand when heated or pressurized to create a more durable surface for striking balls. Golf balls come in different sizes and shapes depending on their use. Game balls are larger than practice balls and have thicker shells to withstand repeated strikes.