The study of nine blends between a polysulfone and a thermoplastic elastomer is presented here. These blends are implemented using an extrusion process without addition of compatibilisant. The main properties required are flexibility and thermal resistance of material. We choose a polysulfone for its properties of thermal behaviour, and interpenetrating network as minority flexible phase. The blends carried out contain 5, 10, 15, 20, 25, 40, 50, 60% of rubber flexible phase. We follow the evolution of the mechanical properties by the study of the storage modulus of blends. The thermal properties come from the change of glass transition temperature of each component in the blend. The stability of the properties of the blends can be connected to their internal morphologies. All these properties can be studied with the traditional techniques of characterisation techniques: dynamic mechanical analysis, thermogravimetric analysis, scanning electron microscopy. Results tend to show the immiscibility of phases in these blends. However, in spite of the presence of two different phases, the blends present interesting mechanical and thermal properties thus a uniform morphology.