Nunclon Treated Tissue Culture Flasks, Filter CapNunclon Treated Tissue Culture Flasks, Filter Cap Specially designed for laboratories where extra security against contamination is necessary Sterile Cap contains 0. 22 mm hydrophobic filter, which prevents wetting and bacteria from growing through membrane while allowing quick, stable buffering in aCO2 incubator. Filter membrane has a three dimensional matrix of polyethylene fibers. Plug seal cap guarantees maximum seal of flask, permitting gas