This work presents the influence of α- and β-Si 3 N 4 seeds on the properties of reaction bonded silicon nitride (RBSN) foams fabricated via wet processing of Si–PMMA–Si 3 N 4 suspensions. Characterization of the seeded foams was performed in terms of porosity, density, and mechanical strength. Phase and microstructural analysis were also used to investigate the influence of α- and β-seeding on the α/β phase ratio and microstructure of the RBSN foams.It was observed that both α- and β-seeds can improve the foam strength by 30% and 85%, respectively, due to more uniform nitridation. A foam strength of 2.23MPa was obtained for RBSN foams seeded with 5wt% α-Si 3 N 4 with a foam porosity of 72vol%. Higher contents of α-seeds create a loose structure of the Si 3 N 4 seed particles within the nitrided matrix resulting in a considerable decrease in foam strength. The addition of 10wt% of β-Si 3 N 4 resulted in the maximum strength of 2.31MPa at a porosity level of 72vol%. The addition of β-seeds also resulted in an increase in the vapor phase reactions during nitridation leading to a significant increase in the β-whisker content of the microstructure. It was observed that even 30wt% of β-seed addition increases the strength of the RBSN foams compared to the unseeded foams.