Oliver-Pharr analysis cannot be used since for time-dependent materials, the assumption of elastic unloading is invalidated by the continuing time-dependent creep deformation and by cohesion, both of which oppose the retraction. Although the unloading curve of binder or mastic may show a steep positive slope, which would traditionally indicate a high stiffness value, this slope is misleading in this situation because time-dependency and cohesive effects interfere with a reasonable application of the Oliver-Pharr method.