Creating a vacuum-tight seal in laboratory apparatuses, the silicone stoppers protect contained solutions and media from being affected by outside elements. The chemically neutral construction is compatible with even abrasive working solvents. With the material also being characteristically resistant to extreme temperatures, the closures will resist cracking when subjected to heating procedures and are autoclavable for reuse. Silicone stoppers have a tapered bottom in various diameter sizes to fit any vessel.