Cushions (also sometimes called “rails”, “rail cushions”, “cushion rubber”, or “bumpers”) are located on the sides of the tables’ rails. There are several different materials and design philosophies associated with cushion rubber. The cushions are made from an elastic material such as vulcanized (gum or synthetic) rubber. The chiefly American jargon "rail" more properly applies to the wooded outer segments of the table to which the cushions are affixed.
The purpose of the cushion rubber is to cause the billiard balls to rebound off the rubber while minimizing the loss of kinetic energy.
The profile of the rail cushion, which is the cushion's angle in relation to the bed of the table, varies between table types. The standard on American pool tables is the K-66 profile, which as defined by the BCA has a base of 1-3/16 inches and a nose height of 1 inch . This[clarify] causes the balls' rebound to be somewhat predictable during game play.
On a carom table, the K-55 profile is used (with a somewhat sharper angle than pool cushions). K-55 cushions have cloth, usually canvas, vulcanized into the top of the rubber to adjust rebound accuracy and speed .
Finally, snooker tables use the K-66 profile, like pool tables, but the cushion is an "L" shape. This is mostly[clarify] because snooker uses balls of a smaller diameter and smaller pocket entrances than does pool.