The process of the liquid outflow from a flat capillary in a nanodispersed composite body into the body bulk have been studied in terms of thermodynamics. An equation for the variation of the Gibbs free energy of a nanodispersed system during this process has been derived and the conditions, under which the interlayers of liquids are either stable or unstable in the bulk of a composite body, have been established. The classes of composite materials, in which interlayers of liquids regardless of the size of refractory particles are stable or unstable are defined.