In this study, a novel portable ultrafine particle counter developed at the University of Cincinnati was tested against a conventional condensation particle counter (CPC, TSI Inc.) for evaluating the efficiency of respiratory protection devices. The experiments were conducted with elastomeric respirators donned on a breathing manikin using combustion particles as challenge aerosols. A favorable agreement between the two data sets on the particle penetration efficiency was observed (slope ≈ 1.16, R2 ≈ 0.99; paired t-test: p-value = 0.91), suggesting that the new counter produced meaningful data comparable to a conventional CPC instrument.