## 3 Results and Analyses
A cleaning pulse was applied when the pressure drop reached 1000 Pa. Fly ash was used for the tests during filtration. The research showed better filtration efficiency for both PM2.5 and PM10 particles for fabrics finished with a PTFE membrane, confirming, at the same time, the massive role of filter material selection in the air purification process. Nevertheless, due to the conditions of using bags and the course of the test that differ from the furniture factory conditions, these results cannot be used to describe the phenomena occurring during the filtration of wood dust in industrial conditions. The variability of the filtration process depending on the type of filter material used was the subject of studies by [PERSON], [PERSON], [PERSON], and [PERSON] (2011) [34]. They studied three types of nonwovens (polyimide PI with polyphenylene sulfide PPS, single polyimide PI laminated with a Teflon layer, and a polyester filter) with the participation of limestone dust and a filtration velocity of 5 cm\(\cdot\)s\({}^{-1}\). The first two nonwovens were heat-treated on the dust side (PI polyimide with polyphenylene sulfide PPS heat-treated dust side, single polyimide PI). Researchers paid particular attention to the formation of a dust layer on the filtering surface. The conducted research showed that the differentiated porosity of the surface of the filtering nonwovens significantly influences the size and strength of the dust layer adhesion. Filter materials subjected to heat treatment or with a membrane were characterized by lower filtration resistance and lower adhesion force of the dust layer, which directly translated into the ease of its removal from the surface. The operation of thermally treated bags was also analyzed in 2017 by [PERSON], [PERSON], and [PERSON] [20]. The test was carried out by the VDI 3926 standard, using dolomite limestone dust and polyester filters with surface thermal treatment, calendering with anti-cracking treatment, and without thermal treatment. The surface of the filter bags and the air humidity during the experiment differed from those used in our experiment (humidity 30%, filter area 227 cm\({}^{2}\)). During the test, the pressure drop (P) on the side of the cleaned air was checked over 50 filtration cycles; the difference between the pulse generation method was that they were activated at a certain pressure drop value and not after five minutes, as was performed in the case of the test of our nonwovens. The filtration velocity during the research was similar to that used in our study and was 4 cm\(\cdot\)s\({}^{-1}\). By examining the filtration efficiency, researchers concluded that the way the surface is treatedhas a significant impact on the efficiency of the filtration process. The untreated (NT) material had a porous surface. The calendered filter material (SCT) had a non-uniform surface with a porous and smooth structure. This was due to processing imperfections in which some areas of the nonwoven fabric were not sufficiently calendered. The nonwovens subjected to calendering and additional anti-pilling (SCT-AP) treatment had an almost entirely smooth and uniform filter surface with fewer elements of high porosity. When analyzing the total time of 50 filtration cycles, it was noted that the surface properties influenced the formation of the filtration resistance. The smoother the surface, the higher the resistance and the higher the filtration efficiency. The impact of various types of dust on the filtration resistance and the development of the K\({}_{1}\) and K\({}_{2}\) coefficient in given operating conditions were the subject of [PERSON]'s research [30] in 2018. Three types of dust (beech, pine, and from a furniture factory) were filtered using the KYS-PROGRES polyester filter material (Remark-KaysSER Polska). The tests were carried out, among others, at the same filtration speed as described in the publication V\({}_{\text{f}}\) = 0.0405 m\(\cdot\)s\({}^{-1}\). The author showed that the type of dust used directly affects the airflow resistance through the filter fabric.