The aim of this study was to evaluate the regeneration efficiency of fibrous filters clogged with metallic ultrafine particles, as several complaints have been made by industrials in the metallurgical field about difficulties linked to the cleaning of filters. Aging of the dust deposits on the filters surface was also reported to be problematic. In this work, the metallic nanoparticles were generated by a pilot thermal spraying process using electric arc. Experiments were conducted on flat filters and the cleaning was performed using reverse pulse-jet. The regeneration efficiency was evaluated according to the residual pressure drop, the removed mass and the cleaned surface. Experiments revealed, under different conditions, a patchy inefficient cleaning of the clogged filters. The cleaning efficiency did not exceed 30 % according to the removed mass. Clogging/unclogging cycles showed that the filtration process is highly instable as the residual pressure drop kept increasing very rapidly. The influence of atmospheric aging, i.e. exposure to different humidity conditions over time, on the filter cakes was investigated. Results showed that in presence of humidity a chemical reaction was responsible for making the deposit more adherent. The regeneration efficiency was reduced to 10 % according to the removed mass after aging for 15 days under 80 % humidity rate. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.