The feed batt is the thick mat of fiber that is fed into the feed section of the card at the back end of the card. The feed batt needs to be as uniform in density as possible. The batt is produced by a card feeding machine that usually has some kind of shaking device to densify the fiber. Sometimes this densification can be produced with a vacuum. Often between the card feed and the card there will be some type of weighing device or density measuring device tied electrically into the feed roll(s) to insure that the amount of fiber fed into the card is consistent in weight.