1 Silicone face mask with exchangeable KN95 filters which can be 3 x refurbished as Personal Protective Equipment instead of a surgical N95 respirator to prevent Sars-CoV2 infections. Running title: Silicone mask with exchangeable filters. Peter Schmid, MD, PhD, FACS General and Vascular Surgeon Private Practice c/o Dr. D. Günthart, Ziegelrain 15 CH 5000 Aarau Switzerland +41 79 415 08 32 ps-vascular@gmx.ch Abstract Initial testing of a Silicone mask with replaceable KN95 filter form Dongguan Deding Com- pany shows the mask to provide a tight fit in most of persons, however, there is need for a bigger size mask for big heads; this bigger Silicone part is in production. Exercising is only possible with the provided filter. Any other filter with a bigger pressure drop prevents breathing while heavily exercising, indicating that the mask fits tightly. It is reasonable to consider China KN95 as "similar" to US NIOSH N95 and European FFP2 respirators for filtering non-oil-based particles like bioaerosols, e.g. viruses (1). The green – white Sili- cone mask filter fulfills the filtration efficiency and the pressure gradient of a KN95 filter as published in GB 2626-2019, implemented on the first of July, 2020 in China (Figure 9). In addition, the filtration efficiency of the green – white replaceable Silicone mask filter for 50nm, 100nm, 250nm, and 500nm neutralized NaCl aerosol particles was better than 95% (Table 5). I used a 5cc syringe with 2 cc of water to be ejected horizontally as fast as possible over a distance of 4 meters against a wall. The ejected water hit in 10 out of 10 attempts the wall. The pressure generated with this setup is certainly higher than 160 mmHg, which is the upper pressure used to validate the penetration resistance to qualify for a surgical mask or a surgical N95 respirator (2). We tested the silicone mask using the same 5cc syringe filled with 2 cc of red ink EcolineR being pushed at full speed from a distance of 30 cm against the silicone mask on my face. There was no penetration of red ink at all. The Silicone parts of the mask can be washed with soap, sprayed with 70% isopropanol, or immersed in 70% isopropanol, and the filters can be exchanged. As a last resort the filter can be refurbished three times using 85 degrees Celsius dry heat for 30 minutes to safely destroy the Sars-CoV2 virus (3); the filtration efficiency for 50nm, 100nm, 250nm, and 500nm neutralized NaCl aerosol particles remains better than 95% (Table 5). This mask may be used as Personal Protective Equipment to bridge periods of shortage during the Sars-CoV2 pandemic.