Hollow, spherical, millimeter diameter scale polymer "micropillows'' (MPs) were fabricated via nonsolvent-induced phase separation/extraction, using a dual layer spinneret extrusion system. Wall thicknesses in the 45-350-mu m range were achieved via the extraction of the n-methyl-2-pyrrolidone (NMP) polymer solvent into a high-molecular weight poly(propylene glycol) nonsolvent. Introduction of heptane into the core of the particles and vaporization of that heptane at elevated temperatures enabled moderate particle expansion and avoided particle collapse after extraction of the NMP solvent. For the most dilute polymer solution feed, the final product was an imidized MP particle with a diameter of about 1.5 mm, a wall thickness of about 45 mu m, and a geometric compression ratio of about 6.0. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 2835-2842, 2011