Indentation hardness
Hardness measurements quantify the resistance of a material to plastic deformation. Indentation hardness tests compose the majority of processes used to determine material hardness, and can be divided into two classes: "microindentation" and "macroindentation" tests. Microindentation tests typically have forces less than . Hardness, however, cannot be considered to be a fundamental material property. Classical hardness testing usually creates a number which can be used to provide a relative idea of material properties. As such, hardness can only offer a comparative idea of the material's resistance to plastic deformation since different hardness techniques have different scales.
Postage stamp paper
Another comparative set of terms refers to the paper's hardness. "Hard", "stout hard", and "soft" have been used to describe the paper. Experts have described the "snap" of the stamp when "flicked" as a means to determine if the stamp was printed on hard or soft paper. A sharper snap implied hard paper because the hardness is a characteristic of the amount or kind of sizing used when making the paper.