Process and apparatus for pneumatically spreading thin graphite or other carbon filaments from a tow bundle to form a sheet or tape in which the filaments are maintained in parallelism. The process includes passing the tow through at least one slot venturi spreader in which the tow is pulled through the spreader in a direction opposite to the direction of primary air flow through the venturi. For certain purposes use is made of first and second spreader units. Each of these units may have at least two side-by-side rows of slot venturies and at least two stacked modules arranged in modular array, whereby to process a plurality of tow bundles simultaneously.