AbstractA series of experiments to investigate the bactericidal efficiency of plasmas acting through porous obstacles was conducted. The purpose was to assess the potential of cold atmospheric plasmas (CAP) for disinfecting and sterilizing objects through different materials, which can open up broad application fields in medicine, hygiene, and packaging. The plasma source was a surface micro‐discharge (SMD) device operating in the atmosphere under ambient temperature and humidity. A 105–106 reduction of Escherichia coli cultures on agar plates was achieved within 60–120 s of plasma application, depending on the material that had to be penetrated (Tyvek, KC fleece, a paper envelope and a medical compress) and on the distance between the bacteria layer and the SMD electrode. Compared with an “open” plasma treatment (without an obstacle) the efficiency was decreased by about a factor 2, a result compatible with the porosity of the materials used. An unexpected finding was that the bactericidal effect was identical with the “open” plasma results when the porous obstacle was placed directly on the electrode. This suggests that the CAP microdischarges were then actually located on the other side of the obstacle – the one not facing the electrode.magnified image