这句话应该是：a material which deforms less under a given load is (stiffer) than one which deforms more.在给定的负荷下,变形小的材料比变形大的材料更有刚度.
其中：a material 是主语,which deforms less under a given load 是定语,修饰主语；is是系词；(stiffer) than one which deforms more是表语.