Different first wall material proposals based on tungsten alloy WNiFe, WLa2O3, W1.1TiC, W26Re, beryllium alloy S-B65, stainless steel SS316 and graphite have been studied in the last years. These materials must be capable of withstanding high temperature and neutron flux. Nevertheless, using hybrid systems, the first wall material choice could influence the criticality system due to the different properties of each material. To analyze this influence, two hybrid reactors were evaluated. The first one is a Tokamak based on magnetic confinement and the second one based on inertial confinement. Both systems contain a transmutation layer with reprocessed fuel spiked with thorium. The results showed the principal nuclides affected in the transmutation layer and the differences in the criticality due to neutron flux variations produced by the changes in the first wall material.