Weight plates have come a long way from simple, flat cast iron plates. Weight plates can be broken down into three basic categories: metal, rubber encased, and bumper plates.
Metal plates can be cast iron or steel. Plates come with 1 inch (standard) and 2 inch (Olympic) center holes to accommodate different sizes of bars. Metal plates can be found in traditional flat styles, or newer styles with cut out grip locations, which make picking up the plates and changing the weighs during your workout much easier. Some newer designs also have more open space to eliminate finger pinching between the plates as you stack, rack, or change your weights.
Rubber encased plates have an aluminum, steel, or cast iron frame depending on the manufacturer and weight of the plate. This frame is coated with black rubber to protect your floors from dropped plates or missed lifts. Rubber encased plates vary in diameter and resemble metal plates in every aspect except the protective rubber coating.
Bumper plates are also rubber encased metal plates, but bumper plates can be black or colored. Colored bumper plates usually have a different color for each weight. Bumper plate all have the same diameter. This is where the colors create an advantage. You can tell the weight of the plate by quickly looking at it, and not have to search for the weight marking.