To educate students about mechanical property of material, we updated a content of practical work. Students learn material mechanics by three points bend of simple beams, and experience to take an idea into a product by making their own model bridge. We used extruded polystyrene (XPS) foam as material. Elastic modulus and Poisson's ratio of the foam was respectively 20 N/mm2 and 0.37 as obtained via tensile tests. It is also revealed that the foam is not strictly isotropic. In the practical work, the relationship between fracture strength of a XPS bridge in three points bend and its shape was discussed for each student's bridge. Based on its questionnaire results, we consider that most students did it with enjoyment.