Addition of fillers in polyurethane foams enhances the mechanical properties of polymeric foams. However, fillers can be loaded to a certain extent, as higher percentage of fillers in polymeric foam causes structural instability leading to the collapse of foam. In this article, we report the use of hollow glass microspheres as a possible co-filler which enables higher loading of nano-clay in flexible polyurethane foam. It has been observed that the structural and mechanical properties of nano-clay-loaded foams were found to cause instability at 5 wt% loading of nano-clay. Therefore, upon addition of hollow glass microspheres in 5 wt%, nano-clay-loaded polyurethane foam shows remarkable enhancement in terms of stability and mechanical properties of the resultant foams. A 100-fold increment in tensile strength has been observed for 2 wt% hollow glass microspheres and 5 wt% nano-clay-loaded flexible polyurethane foams as compared to conventional (unloaded) polyurethane foams. © The Author(s) 2020.