The enthalpy relaxation of PES in the presence of PTFE nanoparticles was investigated and discussed. The increase in the PES glass transition temperature with increasing the PTFE content was explained assuming a frictional effect exerted by the rigid PTFE domains on the PES segmental motions. The presence of constraints on the PES segmental motions caused by the PTFE crystalline domains was confirmed by the analysis of the enthalpy relaxation process. A significant increase in the activation energy and a reduction in the enthalpy lost during PES structural relaxation was observed as a consequence of the PTFE nanoparticles addition, which proves that a potential strategy to reduce physical ageing of non-equilibrium glasses could be the incorporation of rigid, even if non-interacting, fillers. (C) 2013 Elsevier B.V. All rights reserved.