The invention relates to a transparent material which attenuates electromagnetic radiation and/or directly or indirectly ionising particles, of particular use for the production of transparent sheets which serve as protective screens for an operator against said electromagnetic radiation and/or particles. Said transparent attenuating material is made of a matrix of an organic glass in which at least one metal radiation-attenuating compound is dispersed (advantageously other than lead) in the form of nanoparticles, advantageously in the 'core-shell' form. The metals of the nanoparticle metal compounds form at least 25 % of the mass of the material.