Which material property measures resistance to deformation?

Stiffness is the property that measures a material's resistance to deformation when subjected to an applied force. It essentially quantifies how much a material will deform under a given load. A material with high stiffness will show very little deformation when a force is applied, whereas a material with low stiffness will deform more easily. This property is particularly important in engineering and design applications, where maintaining shape and structural integrity under stress is crucial.

Toughness refers to a material's ability to absorb energy and deform plastically before fracturing, which is more about the material's capacity to endure stress than its resistance to deformation under elastic conditions. Electrical resistivity measures how strongly a material opposes the flow of electric current, which is unrelated to mechanical deformation. Brittleness describes a material's tendency to break or shatter without significant deformation, but it does not measure resistance to deformation itself. Hence, stiffness is the correct and pertinent choice for measuring resistance to deformation.