International audience; Plant products arouse great interest in many fields (construction, automotive, textiles, etc …).However, some of their characteristics as their flammability represent major disadvantagesfor some applications. Research is now being conducted in academia and industry to developeffective methods of functionalizing or modifying the surface of these fibers to improve theirperformance. In this respect, radiation-grafting, based on the use of ionizing radiation(gamma or e-beam), represents an interesting method compared to chemical or enzymaticmethods. This technique makes it possible to generate radicals on the fibers allowing thegrafting of molecules of interest, thus offering a large spectrum of possibilities for themodification of the fibers [1][2]. Two ways for grafting under ionizing conditions can beused (Figure 1), pre irradiation and mutual irradiation. In any case, many factors conditionthe success of grafting reactions. In particular, the structure and the composition of thesubstrate influence the nature of the active species formed, and therefore, the feasibility ofthe grafting reaction. Some techniques, such as Electronic Paramagnetic Resonance (EPR),helps us to better understand these parameters, which will be the subject of this presentation.