In some circumstances, electromagnetic compatibility testing must be performed not in a specialized anechoic chamber, but in an open space. However, typical absorbers used in anechoic chambers to absorb incident radiation and to reduce the amount of rays reflected from the walls and the floor, such as ferrite tiles and graphite cones, are not suitable in an open space. In this work, we present the design and a test for the absorbing material, which can successfully be used in a tent or in a similar light and portable structure. The proposed composite material is flexible, has good absorbing and mechanical properties as well as low reflectivity. As an absorber, the nanocrystalline iron alloy with graphite, mixed with an elastomer was proposed. This material was additionally exposed to the ionizing radiation in the dose of 100 kGy in the radioactive gamma source (60Co). The permittivity, permeability, and the shielding properties of the material have been analyzed as well.