Many times a sample contains both volatiles, like plasticizers, antioxidants and UV-stabilizers, and non-volatile fractions. Then it is a good idea to first heat the sample at a relatively low temperature, typically 175 °C, to evaporate the volatile fraction of the sample before pyrolysis at a higher temperature. This is called thermal desorption. The benefit is that the volatile and non-volatile constituents can be analysed separately instead of being mixed up in the same pyrogram.