Series of experimental tests were performed to measure the efficiency of volatile iodine trapping on sand bed filters and metallic filters. These filtering media are used in French nuclear power plants to mitigate releases in case of severe accident. The results show that molecular iodine is more easily trapped than methyl iodide due to its high chemical affinity with stainless steel or with silver and cesium cations included in the filter medium. For methyl iodide, the efficient of trapping is low.