The invention relates to an assembly of parts comprising a first part containing a first polymer composition and a second part containing a second polymer composition, both compositions comprising a semi-crystalline polymer and optionally one or more other components, the first part and the second part being fastened to each other through an interface between the first polymer composition and the second polymer composition, wherein the interface is free from mechanically interlocking elements and the thermal conductivity of the second polymer composition (TC2) is higher than the thermal conductivity of the first polymer composition (TC1) with a factor TC2/TC1 of at least 1.5. The invention further relates to a process for manufacturing such an assembly and to various uses of said assembly.