An apparatus including: (a) a steam generator having a power output of less than or equal to about 6 boiler horsepower; (b) a steam conduit in fluid communication with the steam generator; (c) a fluid material conduit in fluid communication with a source of a fluid material, wherein the fluid material includes unexpanded, expandable polymeric microspheres; (d) a treatment zone in fluid communication with the steam generator via the steam conduit, and with the fluid material conduit, such that the fluid material is contacted by steam within the treatment zone; and (e) a back pressure generator in fluid communication with the treatment zone, capable of increasing pressure in the treatment zone, which results in expansion of the expandable polymeric microspheres when the fluid material exits the treatment zone.