Abstract: A process for the manufacture of flat sheets or webs from a natural fiber material such as cellulose fibers in which the fibers to be processed are first placed on a substrate in the form of a dry heap after which an amount of water not exceeding the amount of moisture which can be absorbed by the fiber is added, whereupon the wetted fibers are subjected to pressure and temperature causing them to bond together forming a sheet or web. When sheets or webs of greater thickness are being made according to the present invention a further step of cooling before relieving pressure is carried out to avoid steam pockets formed within the web from breaking through upon release of pressure.