This invention concerns an improved particulate composition for delivering a drug to the pulmonary system. Applicants disclose a method of identifying an optimal form of aerodynamically light particles which are highly dispersible. The particles of the instant invention are made by creating hollow, spherical drug particles (i.e., progenitor particles) that collapse in the process of particle formation, leading to wrinkled, thin-walled drug particles of very low envelope density. Additionally, Applicants have found that such particles are especially optimal for inhaled aerosols when the surface area parameter (.sigma.) is greater than 2, optimally greater than 3.