The absorption of electromagnetic energy by matter distributed in a predefined loading domain of finite extent is investigated in its general aspects. It is shown that under variation of the medium properties in the loading domain, the electromagnetic energy absorbed by the load can, at least in principle, be maximized. The maximization condition serves as constitutive relation, in a nonstandard form, for the relevant medium. The condition is a configurational property and is independent of the distribution of the sources that generate the exciting electromagnetic field.