Vented Polyethylene Cap for Falcon® 175cm² Flasks contains a 0.2 µm membrane vent that allows consistent gas exchange but prevents passage of bacteria and fungi. Bulk, Sterile, 50/case Material Cap: Polyethylene Vent: 0.2 µm gas permeable membrane Vented caps minimize contamination associated with standard open incubation. The vented caps prevent media that can become trapped in a partially opened cap from blocking gas exchange. The caps will not fall off in the incubator because of vibration.