Draft is simply the measurement of the speed difference between two elements of a nonwoven machine. These could be rolls, conveyors, or other moving elements. Draft is usually expressed in percent. Draft can be positive or negative. Positive draft means that the following element is going faster that the preceding. Negative means that the following element is going slower.
As an example look at the nip rolls below. The first set of rolls has a surface speed of 100 feet per minute. The following set has a surface speed of 110 feet per minute. Draft is calculated by the formula: (Following speed-Preceding speed)/Preceding speed. In this case: (110-100)/100 which is 10/100 which 0.1 and expressed as a percent is 10%.
It is important to remember that as draft occurs throughout the machine, the fabric is stretched and the weight of the fabric is reduced. In the example below the weight of the fabric at the first nip rolls is 5.0 oz per sq yd. It is stretched between the rolls and comes out of the second nip rolls 10% lower in weight at 4.5 oz per sq yd. It is not unusual to have 200% or more draft in a nonwoven line from beginning to end.