Optical properties of core–shell (metal) nanoparticles and composites based on them were investigated in the classical approximation. Frequency dependences of the real and imaginary parts of the dielectric permittivity of bilayer particles and absorption coefficients of composites based on them were calculated. Small-scale oscillations of the real and imaginary parts of the dielectric permittivity and absorption coefficient were found in the low-frequency spectral region. The behavior of the dielectric permittivity of bilayer nanoparticles was analyzed for the limiting cases of thin and thick shells. The influence of the effective mean free pathlength of electrons on the optical characteristics of the bilayer nanoparticles was considered. Two maxima of the composite absorption coefficient were demonstrated to be due to hybridization of polar modes.