To construct an item with structural integrity, an engineer must first consider a material’s mechanical properties, such as toughness, strength, weight, hardness, and elasticity, and then determine the size and shape necessary for the material to withstand the desired load for a long life. Since members can neither break nor bend excessively, they must be both stiff and tough. A very stiff material may resist bending, but unless it is sufficiently tough, it may have to be very large to support a load without breaking.