Abstract: A preform of complex three-dimensional shape is prepared by a directed fiber preforming process in which a flow of chopped fibers are drawn by vacuum against a foraminous screen having a shape corresponding to that of preform to be made. The screen has depressed regions that are susceptible to excessive build-up of the chopped fibers. To counteract the build-up in these areas, a baffling system is provided behind the screen having baffle plates which are extendable into and out of blocking engagement with the backside of the problem depressed regions to govern the vacuum draw and hence the deposit and build-up of fibers across the depressed regions.