Surf breaks can be grouped according to their intensity. There are two variables to consider in determining the intensity of a surf break: the shape of the tube and the angle of the peel line. Tube shape indicates the degree of upthrust, which is roughly proportional to the volume of water being thrown over with the lip. The angle of the peel line reflects the speed of the tube. A fast, "down the line" tube has a peel line with a smaller angle than a slower, "bowly" tube.