In this study, the parameters which influence strength of the open-cell reaction bonded silicon nitride foams were investigated. These parameters include the monomer content in the suspension, the porosity level of the foam, the nitriding atmosphere including N-2 and N-2-4 %H-2, and the nitriding temperature ranging from 1350 to 1425 A degrees C. The nitriding mechanisms dominating under different nitriding conditions were also studied based on the phase and microstructural analysis. It was observed that there is a minimum monomer concentration of 25 wt% required in the premix solution to obtain a defect-free and homogeneous RBSN foam. Increasing the monomer content only from 15 to 20 wt% resulted in a threefold increase in the foam strength. The high porosity level of the foam which is above 70 vol% significantly affects the nitriding mechanisms and microstructures compared to those of dense RBSN ceramics. The maximum strength was obtained for the foams nitrided under N-2-H-2 atmospheres, and the nitriding temperature had a negligible effect on the foam strength when H-2 is present in the atmosphere. alpha-Si3N4 is also the dominant phase in the microstructure in the presence of H-2 regardless of the nitriding temperature. It was observed that beta-Si3N4 can also be present in high quantities when N-2 atmospheres are used. beta-Si3N4 is present in the microstructures in two different morphologies including interlocking rods and angular grains. Each morphology forms based on a specific nitriding mechanism.