The objective of this study was to assess how the relative efficiency of N95 respirators and surgical masks might vary with different challenge aerosols, utilizing a standardized manikin head form as a surrogate to human participation. A Collision nebulizer aerosolized B. anthracis Sterne strain endospores and polystyrene latex (PSL) particles to evaluate 11 models of N95 respirators and surgical masks. An automated breathing simulator, calibrated to normal tidal volume and active breathing rate, mimicked human respiration. A manikin head form with N95 respirators or surgical masks, and manikin head form without N95 respirators or surgical masks were placed in the bioaerosol chamber. An AGI-30 sampler filled with phosphate buffered water was fitted behind the mouth of each manikin head form to collect endospore bioaerosol samples. PSL aerosols concentrations were quantified by an ARTI Hand Held Particle Counter. Geometric Mean (GM) relative efficiency of N95 respirators and surgical masks challenged with endospore bioaerosol ranged from 34-65%. In PSL aerosol experiments, GM relative efficiency ranged from 35-64% for 1.3 μm particles. GM filtration efficiency of all N95 and surgical N95 respirators filter media evaluated was ≥99% when challenged with particles ≥0.1 μm. GM filtration efficiency of surgical mask filter media ranged from 70-83% with particles ≥0.1 μm and 74-92% with 1.3 μm PSL particles. Relative efficiencies of N95 respirators and surgical masks challenged with aerosolized B. anthracis endospores and PSL were similar. Relative efficiency was similar between N95 respirators and surgical masks on a manikin head form despite clear differences in filtration efficiency. This study further highlights the importance of face seal leakage in the respiratory protection provided by N95 respirators, and demonstrates it on a human surrogate.