The screw cap can be tightly closed as the membrane permits an automatic sterile gas exchange, allowing safe pressure equalisation during the autoclave cycle, and at the same time ensuring the sterility of the bottle contents. DURAN® Original GL Screw Capped Laboratory bottles are ideal containers for sterilising and storing media or buffer solutions. However, it is strongly recommended that during the autoclaving cycle the caps are only loosely tightened. Heating times are reduced if the steam is easily able to penetrate the contents of the bottle. Loose caps also reduce the risk of failure due to pressure build up inside the bottle, which can reach 400 kPa (absolute). In addition, tightening the screw caps immediately after autoclaving, will result in a vacuum caused by the cooling of the steam. This can lead to bottle failure, and is an especially important consideration for larger bottles. To overcome these limitations, the sterile venting membrane screw caps were developed.