Depth filtration is a widely utilized mechanism for submicron aerosol filtration using disposable filter cartridges and facemasks. The filter media should be carefully engineered to reach high filtration efficiency and dust-loading capacity at the expense of a low-pressure drop (ΔP). Filter media with bimodal fiber diameter distribution enhance particle capture by creating small pores with tiny fibers, while microfibers improve airflow, reduce ΔP, and increase the effective filter area for particle retention. In this study, bimodal filters were achieved through the homogeneous distribution or layered use of nanofibers and microfibers. The impact of the bimodal design was explored using fibrous mats produced through melt-blowing, solution-blowing, and electroblowing methods. Keeping the basis weight of filter samples at 30 gsm, using four-layered filters (4L) improved air permeability compared to single-layer samples. The 4L sample exhibited the highest performance, achieving 99.52% efficiency at 148 Pa. Moreover, replacing the melt-blown layer with bimodal mats in the 4L design increased the filtration efficiency to 99.61% keeping ΔP nearly the same. The corona discharge treatment yielded the highest efficiency (99.99%) in the 4BML sample, even after 1 month the efficiency was maintained at 99.90%, highlighting the advantage of bimodal fiber distribution in electret filters. Highlights: Four-layered filter (4L) structures resulted in improved air permeability. Bimodal layer (BL) achieved by adding SB nanofibers into the melt blowing. BL in 4L structure increased the efficiency from 99.52% to 99.61%. Modified BL sample (4BML) provides the highest QF (0.044 Pa−1) after 1 month.