An alternative indentation method to study materials that present a time-dependent behaviour (e. g. viscoelasticity) is the dynamic stiffness measurement technique, which provides fast and accurate values of the elastic properties through the calculation of the storage modulus (related to the elastic recovery of the material), and the loss modulus (related to the damping), using indentation cycles with oscillating load or displacement. We have made dynamic measurements on four amorphous materials (CNx, amorphous carbon, fused silica and polypropylene). Such materials have a relatively low density compared to crystalline materials of similar composition and atoms are able to move into internal free space during deformation. The results suggest that all the amorphous materials have a similar time-dependant behaviour associated with the restrictions to movement of atoms (or chains) by neighbouring atoms in the amorphous structure.