There are primarily two methods of making webs from staple fiber: carding and airlaid. Where a card makes a thin web of parallelized fibers, an airlaid machine can make a significantly thicker web in which the fibers are quite randomized in orientation. On an airlaid machine a lightweight web might be 50 gsm and 6 mm thick and a heavy web might be over 3000gsm and 150 mm thick. Of course output speed of the machine is much slower at the heavy weights.
On the input end of an airlaid machine there is a feedroll and feedplate feeding fiber to a high speed lickerin. The fibers are then knocked off the lickerin by a high speed stream of air. The fibers are carried by this air stream and deposited on either a moving conveyor that is made of fine, porous mesh or onto a rotating porous condensing drum. Inside the drum or conveyor is a vacuum that is slightly stronger that the air stream carrying the fibers. Thus the fibers are pulled onto the drum or conveyor and held fast until the drum or conveyor moves forward to a spot where there is no longer any vacuum. The formed web is then conveyed to the next element of the nonwoven line, which is usually some type of bonder.
Airlaid machines are capable of handling many types of fiber that cannot be carded effectively including metals, hair, fiberglass, and many types of cellulosic fibers.