The kinematic and thermal coupling between pyroclasts and gas is one of the main controlling factors in the dynamics of explosive volcanic eruptions. Here, we performed rapid decompression experiments in a shock-tube apparatus at eruptive pressures (2–11 MPa) using monodisperse volcanic particles (grain-size 0.063–1.4 mm). We systematically investigated the coupling of these particles with the gas phase by measuring the rarefaction speed and the ejection velocity of the particles front in each experiment. The results are consistent with a theoretical model derived from the pseudogas approximation (i.e. perfect coupling) only for particles smaller than a certain size: ∼ 0.125 mm for rarefaction speed and ∼ 0.5 mm for the particles front ejection velocity, whereas larger particles are significantly decoupled. We present an experimental parameterization to calculate the kinematic Stokes number (Stk). We show that: 1) for the ejection process the particles are coupled with the gas if Stk < 1, whereas for the rarefaction speed the particles are fully coupled when Stk < 0.2; 2) for the rarefaction speed there is a transition when 0.2 < Stk < 1; and 3) in both processes particles are decoupled when Stk > 1. Furthermore, where the Reynolds number based on the relative velocity between gas and particles (Rep) is larger than 103, the ratio between the timescales required for thermal and kinematic equilibration increases with Rep, such that some particles are coupled with the gas but decoupled from it thermally. These findings represent the first experimental delineation of kinematic and thermal coupling regimes between volcanic particles and gas and contribute thereby to a more robust basis for multiphase explosive eruptive models.