Also known as rubber bungs, rubber stoppers are used to seal bottles, tubes and many other containers. They plug containers from the outside without displacing the volume inside.

Some more resistant stoppers can also be used for heavy industrial processes.

Stoppers can be straight-edged, but mainly they have tapered sides. The bungs are partially inserted into a vessel acting as a seal. The stoppers are often used in laboratories and other scientific settings, primarily to seal test tubes and other flasks. Scientists can connect these flasks to other apparatus using tubes which are inserted into small holes in the bungs.

Slightly elastic bungs are perfect for preventing gases and liquids from escaping. They can also help protect important products against contamination.

Choosing The Right Size Bung

The following bungs are all tapered, meaning they have wider tops than bottoms. This means the bungs fit more securely on a wider range of containers.

Rubber bungs need to fit tightly in their container opening so you need to pay close attention to the size of your bungs.

Ensure that the diameter of your container opening fits between the top and bottom diameters, so you can be sure of a tight fit for your bung.

Red Rubber Bungs

Red rubber stoppers are mainly used in chemical laboratories in flasks and test tubes, but they can also be used in fermentation processes, for example in wineries.

Made from natural rubber, it uses polymers of the organic compound isoprene and is classified as an elastomer meaning it has a high stretch ration and high resilience. It is also extremely waterproof.

All the bungs are available with or without drilled holes, except the 3mm and 4mm red rubber bungs, which are too small to be drilled.

Other equipment such as glass tubes – connected to other lab apparatus - can be plugged into the rubber stopper holes.

Bungs with a bottom diameter between 5mm and 8mm are available with one hole of 3mm. Any bung with a bottom diameter over 9mm can have one hole of 5mm and any bung over 15mm can have two 5mm holes.

To help identify a bung’s size, each stopper has a moulded number which corresponds to the bottom diameter of the bung.