The intricate interplay between humidity and temperature on PM filter performance has remaineda subject of profound scientific interest. By employing fully-automated weighing method anda two-factor regression model, the study aimed to evaluate mass variations of unloaded PM filtersunder diverse humidity and temperature conditions. Existing guidelines, as posited by the USEPA and the European Standard (EN), have demonstrated a pronounced disparity. The US EPAadvocates a narrow humidity range of 30–40% RH, while the EN suggests a broader range of40–50% RH. The results of this investigation confirm the US EPA’s guidelines, which exhibitedsuperior filter mass stability under varying humidity. In controlled stable temperature conditionsof 20C, the research unveiled significant variations in filter mass as RH% increased from 50%to 55%. It has been proven that under stable temperature conditions (20C) inside a weighingrobot, an increase in relative air humidity from 50% to 55% results in filters mass addition by15 μg (Q, quartz fibre filters); by 93 μg (PTFE filters); by 9 μg (G, glass fibre filters); by 112 μg (PA,polyamide filters) and by 20 μg (PC, polycarbonate filters). Further exploration of the conditioningranges prescribed by the EN 12341:2014 standard, the study highlighted glass fibre filters as beingnotably stable, while polyamide membrane filters posed intriguing challenges potentially relatedto ionization insufficiencies during the equilibration stage. These findings bear significance forfilter manufacturing and conditioning protocols, potentially enhancing the precision of air qualitymonitoring practices.