To cope with the shortage of filtering facepiece respirators (FFRs) caused by the coronavirus disease (COVID-19), healthcare institutions have been forced to reuse FFRs using different decontamination methods, including vapor hydrogen peroxide (VHP). However, most healthcare institutions still struggle with evaluating the effect of VHP on filtration efficiency (FE) of the decontaminated FFRs. We developed a low-cost in-house FE assessment using a novel 3D-printed air duct. Furthermore, we assessed the FE of seven types of FFRs. Following 10 VHP cycles, we evaluated the FE of KN95 and 3M-N95 masks. The 3M-N95 and Benehal-N95 masks showed significant lower FE (80.4-91.8%) at fine particle sizes (0.3-1 microm) compared to other FFRs (FE >/= 98.1%, p < 0.05). Following 10 VHP cycles, the FE of KN95 masks was almost stable (FE stability > 99.1%) for all particle sizes, while 3M-N95 masks were stable only at 2 and 5 microm (FE stability > 98.0%). Statistically, FE stability of 3M-N95 masks at 0.3, 0.5, and 0.7 microm was significantly lower (p </= 0.006) than 2 and 5 microm. The in-house FE assessment may be used as an emergency procedure to validate the decontaminated FFRs, as well as a screening option for production control of FFRs. Following VHP cycles, both masks showed high stability at 5 microm, the size of the most suspected droplets implicated in COVID-19 transmission.