Ethylene propylene diene monomer (EPDM) rubber based bio-composites filled with silane-modified wood fiber (SiWF) were foamed by using chemical foaming method. The SiWF and the incorporation of dicumyl peroxide (DCP) generated crosslinking in the developed EPDM bio-composite foams, which showed much lower water absorption and improved thermomechanical properties. With SiWF and in situ cross-linking, the tensile strength and modulus of EPDM bio-composite foams exhibited up to 90% and 600% enhancement compared to the unfilled foam, respectively. The compressive strength and modulus individually showed up to 170% and 600% increase. The developed bio-composite foams also displayed lower apparent thermal conductivity than the unfilled EPDM foam over the heating temperature range, showing possible applications as insulation materials.