A thermally expandable microcapsule or microsphere is a physical foaming agent that expands with heat. Featuring a foaming core-shell structure surrounded by a polymer shell at the core, expandable microspheres expand up to five times their diameter when brought to optimum temperatures to form extremely small but independent bubble cells. MS 197D product is especially preferred in PVC slipper and shoe sole applications. The particle size averages 25 microns and is suitable for working between 165°C and 195°C.