In chemistry, bungs made of hardened rubber are frequently used in small-scale experimental set-ups involving non-corrosive gases. Some chemistry bungs may also include one or more holes so a glass tube or laboratory funnel may be inserted through the bung and into the container or another piece of apparatus. The rubber bung may be used to seal a flask because the user may require the contents to be mixed via shaking the flask or may require that the contents be kept inside the flask and prevented from leaking out. In all cases, the bung keeps the experimentation environment sealed so that liquids or gases cannot escape (or enter).