This paper focusses on the presence of visible synthetic materials (plastics) and finishes from the 1960s in the interior of office buildings. Although the ongoing research on synthetic materials as art pieces is well developed, building components from the interior and exterior of Belgian patrimony have not yet been studied, and remain undervalued as integral components of heritage buildings. The research presented in this paper tackles this issue by examining two specialized Belgian journals, namely La Technique des Travaux and La Maison. A selection of case studies from these two journals was examined in-depth to assess general tendencies and obtain a thorough evaluation and validation of the visible plastic materials and finishes in the case studies: the floor, wall and ceiling finishes. The plastic elements of listed monuments have often been removed, and do not receive a similar level of protection to other materials. Plastic heritage is not valued and protected as a relevant part of recent historic architecture. This part of the built patrimony needs to be recognized with equal status and therefore conserved.