The purpose of the present work has been to produce knowledge as regards the rheological behavior of polymer matrix in nonwoven fibrous reinforcing structures for composites. The results are expected to contribute toward a better understanding of flow mechanisms in fibrous systems in order to develop better techniques for fabricating elastomer‐based composites. Theoretical and experimental analyses have been made of interactions between the structural parameters of the fibrous mats and the flow characteristics of the matrix with systematically varied material and process parameters. In nonwoven mats with fibers laid lengthwise, the flow rate along the fiber direction was found to be significantly higher than the flow rate crosswise to the fiber direction. Nonwoven mats with multidirectionally laid fibers exhibited a practically radial flow front pattern. Nonwoven mats made of coarser fibers showed greater matrix polymer flow rate as compared with finer fibers. The matrix flow distance was proportional to the logarithm of injection time. The decrease of pressure in the mold cavity was linearly proportional to the matrix flow distance. The dependence of permeability on the level of compression of the fibrous structure is in agreement with the results published by other workers.