This study provides predictable flow behavior of a hybrid biocomposites made from kenaf/coir reinforced unsaturated polyester using the Moldflow software. A medium size electrical part has been chosen as a mold having multi-wall thicknesses and complex surfaces. Three different shapes of charges of the bulk molding materials were used and compressed into the mold part. The shapes of charges would be rectangular, cubic and cylindrical shapes. The results showed that rectangular charge took 0.2 seconds to fill up the part while the cubic and the cylindrical charges took 1.911 and 2.898 seconds respectively. After 70 seconds the conversion at nodes was more than 98% for all charges. On the other hand, the final densities were 1.88 ± 0.08 g/cm3 for all charges. The cubic charges showed a better temperatures distribution at flow front followed by rectangular, the last being the cylindrical charge, and the average shrinkage was 5-7% for the charges. The cubic shape showed good fibers orientation to the flow direction of the bulk materials followed by cylindrical charge while the rectangular charge showed poor orientation of fibers affected on the deflections, weld lines and air traps in the internal part. For the rectangular, the charge showed more critical weld lines and more air traps especially on the surface of the molded part and more deflections on the corner edges. But, the cubic charge showed the lowest deflections rate, air traps and weld lines defects.