It was found that the fiber loading increased thermal stability of the biocomposite. The first mass loss, in the range 31-100°C, is due to evaporation of moisture. Then the mass loss between 150°C and 380°C for SPF/SPS biocomposites, are due to the decomposition of the three major constituents of the natural fibers; hemicellulose, cellulose and lignin.94 In general, the thermal decomposition of these fibers consists of four phases. The first phase was decomposition of hemicelluloses, followed by cellulose, lignin and lastly their ash.9596 Yang et al.97 reported that hemicelluloses decompose at 220°C and substantially completed at 315°C. As soon as hemicel­luloses had completely decomposed, the decomposition of cellulose will take place as the second phase of decomposition. Because of its highly crystalline nature of their cellulose chain than amorphous, cellulose has relatively thermally stable. It does not start to decompose until hemicelluloses had completely decomposed which normally starts at higher temperature at about 315°C.97 This is supported by Kim et al.98 where they reported that the critical temperature of decomposition of crystal­line cellulose is 320°C. The third phase was the decomposition of lignin. It is the most difficult to decompose compared to hemicelluloses and cellulose. Although the decomposition of lignin had started as early as 160°C, it decomposes slowly and extends its temperature as high as 900°C to complete its decomposition.97This is contributed by lignin which is very tough component and known as the compound that gives rigidity to the plant materials. Finally, when the lignin had completely decomposed, the component that is left is inorganic material in the fibers which can be assumed as ash content. This is due to the presence of inorganic materials such as silica (silicon dioxide, SiO2) in the fiber which can only be decomposed at a very high temperature of 1723°C. The increase of fibers increased the lignin and ash content, compared to pure plasticized SPS. It was found that the lignin and ash content of SPF was 31.5% and 4%, respectively.99 The large degradation at 310 °C appears for plasticized SPS are due to the elimination of the polyhyroxyl groups, accompanied by depolymerization and decomposition in starch.100