Hardness is a measure of how resistant solid matter is to various kinds of permanent shape change when a force is applied. Macroscopic hardness is generally characterized by strong intermolecular bonds , but the behavior of solid materials under force is complex; therefore, there are different measurements of hardness: scratch hardness, indentation hardness, and rebound hardness.
Hardness is dependent on ductility , elastic stiffness , plasticity , strain , strength , toughness , viscoelasticity , and viscosity .
Common examples of hard matter are ceramics , concrete , certain metals , and superhard materials , which can be contrasted with soft matter.