Polymer network composition comprising a semi-crystalline covalently crosslinked polymer network including exchangeable covalent bonds and crosslinking bonds and at least an exchange reaction catalyst, wherein the number of crosslinking bonds is sufficient for the polymer network to be beyond the gel point and the number of exchangeable bonds is sufficient for the network to relax stresses and/or flow when conditioned at an appropriate temperature. Such compositions are characterized by the fact that the network is able to reorganize by exchange reactions that allow it to relax stresses and/or flow while maintaining network connectivity.