This paper examines the development and consequence of flow structures and possible defects arising in multiple shot injection or multiple-gated injection of two-component resins mixed in-line into a mold with and without fiber preforms. This work may also be relevant to the packing stage. Experiments were run where a premixed batch of vinyl ester resin with peroxide and tracer dye, displaces another older batch of premixed resin in a mold. Polymerization of resin as it flows through the preform during the filling stage sets up an increasing viscosity profile along the fluid filled region and viscous fingering is observed as expected. The types of flow patterns associated with this phenomenon have been explored with random and woven fibrous media packed in a clear mold. The molded plaques were cut up and tested in 3-point bend so that the flexural moduli of specimens with various flow structures could be compared. The flow structures observed include fingers with rounded ends and fingers with multiple tips. Such flow structures lead to regions in the plaques where ＇packets＇ of fluid with different extents of polymerization due to differences in age are juxtaposed prior to gelation of the resin. It was found that finger structures with several sharply defined interfaces tended to decrease the value of the flex modulus by up to 32%, depending on the preform characteristics. Multiple finger tips with diffuse boundaries do not seem to be detrimental to the flex modulus, but multiple tips with sharp boundaries have lowered the flex modulus by 32%.