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.

There are different types of rubber stopper:

They have different properties. This guide explains the benefits of each material and shows what should be used for each purpose.

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.

This product is manufactured to standard: BS2775:1978 (1992).

Red rubber bung size guide

Product Code

Bottom Diameter (mm)

Top Diameter (mm)

Length (mm)

RB003

3

4.5

12

RB004

4

5.8

14

RB005

5

7

16

RB006

6

8

16

RB007

7

9

16

RB008

8

10.5

20

RB009

9

11.5

20

RB010

10

12.5

20

RB011

11

14

24

RB013

13

16

24

RB015

15

18

24

RB017

17

20.3

26

RB019

19

22.5

28

RB021

21

24.5

28

RB023

23

26.5

28

RB025

25

28.5

28

RB027

27

31

32

RB029

29

33

32

RB031

31

36

35

Neoprene rubber bungs

Grey neoprene rubber stoppers can be used in tubes and bottles in the same way as the red rubber bungs.

Neoprene is a synthetic rubber with better chemical stability and heat resistance over a broad range of temperatures. It is used in a lot of processes – it can be used as electrical insulation and in other hostile environments.

The solid version of neoprene can be used as a bung because it has good resistance to petroleum based oils and other chemicals as well as ozone. It can also be used across temperatures ranging from -30°C to 100°C.

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.

This product is manufactured to standard: BS2775:1978 (1992).

Neoprene rubber size guide

Product Code

Bottom Diameter (mm)

Top Diameter (mm)

Length (mm)

NB005

5

7

16

NB008

8

10.5

20

NB010

10

12.5

20

NB011

11

14

24

NB013

13

16

24

NB015

15

18

24

NB019

19

22.5

28

NB021

21

24.5

28

Translucent silicone stoppers

Manufactured from high-grade silicone, these plugs can be used at a huge range of temperatures – from -70°C to +250°C.

This means they can be used for heavy industrial processes and in environments where they will be exposed to extremes of temperature. They are also good resistant properties against acids, alkali solutions and weathering.

Hilltop Products stocks a huge range of sizes, so you can be sure to find one that fits your needs.

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.

This product is manufactured to standard BS2775:1978 (1992).

Translucent silicone stopper size guide

Product Code

Bottom Diameter (mm)

Top Diameter (mm)

Length (mm)

SB003

3

4.5

12

SB004

4

5.8

14

SB005

5

7

16

SB006

6

8

16

SB007

7

9

16

SB008

8

10.5

20

SB009

9

11.5

20

SB010

10

12.5

20

SB011

11

14

24

SB013

13

16

24

SB015

15

18

24

SB017

17

20.3

26

SB019

19

22.5

28

SB021

21

24.5

28

SB023

23

26.5

28

SB025

25

28.5

28

SB027

27

31

32

SB029

29

33

32

SB031

31

36

35

SB033

33

38.5

38.5

SB035

35

40.5

38.5

SB037

37

42.5

38.5

SB039

39

44.5

38.5

SB041

41

47

42

SB043

43

49

42

SB045

45

51

42

SB049

49

55

42

SB053

53

59.5

45.5

SB057

57

64

49

SB062

62

69

49

SB067

67

74

49

SB071

71

78

49

SB075

75

85

54

For more information about any stopper product, speak to a member of our knowledgeable sales team. Call: 01942 723 101.