The behavior of polymer melts in the presence of solid walls has been studied by recording the displacement of differently colored melts of the same stock in a capillary rheometer before and after flow. For emulsion PVC (E-PVC) without lubricant and plasticizer it was found that at T = 443°K there is almost complete slip at the wall (metal). Slip of both E-PVC and suspension PVC (S-PVC) gradually decreases with increasing temperature. Since this is a reversible phenomenon it cannot be directly related to the particle structure, which disappears irreversibly with increasing temperature. For S-PVC it was further found that slip increases with increasing pressure.