Thermal decomposition of WPC depends on wood species, amount of wood, particle size, moisture content, quantity and type of polymers, coupling agents, lubricants and other additives. Hemicelluloses, cellulose and lignin primarily decompose between 150–350◦C and 250–500◦C whereas the thermal degradation of PP and HDPE begins at 472◦C respectively 517◦C [13]. Therefore, TGA can be used for quantitative determination of WPC components (wood and thermoplastic) if the components are known. For this purpose, a TGA method was developed in this project for three WPC formulations with 50% and 70% wood filler, respectively, by using inert and reactive purge gases and by optimizing heating rate, dynamic and isothermal heating and duration of isothermal steps.