In the last few years, the mechanical response of hollow thermoplastic microspheres-elastomer matrix composites has been investigated. The large majority of the studies focuses on their compressive properties and particularly on the stress-strain response. In the present paper, large strain uniaxial tension experiments are conducted on thermoplastic microspheres filled polyurethane elastomer. Six volume fractions of microspheres are considered. Thanks to a two-camera setup and digital image correlation measurements, the volumetric response of the materials is extensively analyzed. As a major result, the remarkable volumetric behaviour is highlighted: the hydrostatic pressure vs. volume change curves admit several extrema that may be read as the macroscopic signature of the complex microstructural phenomena involved during deformation. Moreover, it is shown that the size of the volumetric loading-unloading hysteresis loop is directly related to the volume fraction of microspheres in the materials.