To measure a material’s stiffness or resistance to deformation, we use what is called a “modulus of elasticity”. For reference, easily pliable materials like polystyrene foam or rubber have modulus of elasticities of less than 1 GPa (gigapascals) whereas concrete has measure of right around 30 GPa. Both steel and carbon fiber measure upwards of 200 GPa (Zoltek PX35 is 242 GPa for the record) which, at first glance might suggest they are roughly equal to one another in terms of strength.