This study deals with the hydrostatic strength of hollow glass microspheres composites, commonly known as syntactic foams, using model materials made of 0.15 g/cm3 microspheres with 3 types of matrix, two epoxies and one paraffin. More than 100 model material samples are characterized for that work. The hydrostatic strength of these composite materials is determined in a pressure vessel, which can go up to 100 MPa. Two major parameters are studied: stiffness of the matrix and microsphere volume content within the composite material. The results clearly show that the hydrostatic strength of the syntactic foam can be improved by an increase in matrix stiffness or a reduction in microspheres content. Based on experimental data an empirical model with two parameters is proposed to describe the hydrostatic strength of syntactic foam. The relevance of the model is discussed.