We discuss the technology developed at the Lebedev Physical Institute for the manufacture of hollow microspheres polyethylene terephthalate (PETP). The microspheres are produced by means of foaming solid PETP granules containing CO2 blowing agent in a vertical free-fall furnace. The diameter of obtained microspheres ranges from 50 to 800 µm, with aspect ratio typically from 10 to 50. Reasonably high maximum rupture strengths and relatively low permeabilities have been measured. These properties allow PETP microspheres to be used for long-duration storage of gases and in the technology of cryogenic targets for the ICF program.