gummistopp

A gummistopp is a rubber stopper used to seal openings in laboratory glassware, bottles, and vessels. In English it is commonly referred to as a rubber stopper. The term is used in several Nordic languages to describe a flexible, compressible plug that fits into an opening to prevent the passage of liquids or gases.

Most gummistoppes are made from natural rubber or synthetic elastomers such as nitrile, neoprene, or silicone. They come in a range of sizes to fit standard joint sizes, neck diameters, and opening dimensions. Some stoppers are solid, while others are drilled with one or more holes to accommodate thermometers, tubes, or adapters. Specialized variants include ground or reamed stoppers for a tighter fit, or stoppers with embedded core materials like PTFE to improve chemical resistance.

Common applications include sealing standard laboratory flasks, beakers, test tubes, and reaction vessels. They are also used in fermentation equipment, sampling devices, and certain household or hobby contexts such as home brewing or aquariums, where a flexible seal is required. The choice of material depends on chemical compatibility, temperature exposure, and required durability. Natural rubber offers good elasticity and cost efficiency but may swell or degrade with certain solvents; silicone provides high temperature resistance and chemical inertness but at a higher cost; nitrile and neoprene offer good chemical resistance for many lab solvents.

Maintenance involves cleaning after use and ensuring the stopper is dry before storage. Some gummistoppes are autoclavable, particularly silicone and some nitrile types, while others must be cleaned and stored to avoid degradation. Safety considerations include avoiding solvent exposure that could weaken the material and inspecting for wear or cracks before reuse. See also stopper, cork, and laboratory glassware.