Sulfur Hexafluoride: Sound Thickening Gas (SF6)

Have you ever heard the sulfur hexafluoride? You must have seen videos of people thinning their voices by inhaling helium. Today, we will examine a gas with the opposite effect of helium. Also known as anti-helium, the name of this gas in the chemical world is sulfur hexafluoride. So, what is this gas, and how does it thicken our voice?

SF6 (Sulfur Hexafluoride)

Sulfur hexafluoride is an inorganic compound with the formula SF6. It is an odorless, colorless gas and is not flammable. This compound, which has sulfur in its center, has six fluorine atoms around it, thus having an octahedral geometry. It is a nonpolar gas and is insoluble or only slightly soluble in polar solvents such as water. Just like helium, this gas is liquefied and transported through tubes.

How does it make the sound thicker?

Sulfur hexafluoride is much denser than air. Air has a density of 1,225 g/L at sea level conditions. SF 6 is about five times denser than air, with a density of 6.17 g/L. Because of this higher density, sound travels more slowly in the air. If we fill a balloon with sulfur hexafluoride and inhale it into our lungs, our voices will deepen. It achieves a more robotic, even Darth Vader-like tone.

On the other hand, Helium has the opposite effect, as it is a much less dense gas than air. It thins our voice by allowing the sound to spread faster. Both gases mix into the air during our normal breathing in a short time, and our voice tone returns to normal. To see the difference between the two gases, you can watch the Mythbuster team’s fun video about it:

We have to make a warning here. Yes, we mentioned that sulfur hexafluoride qualifies as a non-toxic, inert gas. However, there are risks, such as hypoxia (oxygen deficiency) and fainting. At the same time, sulfur hexafluoride is classified as a mild anesthetic. Therefore, care must be taken when using both SF6 and helium. These gases should not be inhaled for a long time.

sulfur hexafluoride sf6

Soaring Ships? How?

Another fun and impressive experiment with SF6 is to fill a large storage container with this gas and throw a paper ship into it. Don’t worry, SF6 will not go out of the container as it is heavier than air. Since it is a transparent gas, an outsider will not notice it, and the paper vessel will not hit the bottom when placed inside the storage container. As seen in the gif below, it will float on the gas and create the appearance of watching a flying ship.

Aluminum foil vessel dropped on container filled with sulfur hexafluoride
Aluminum foil vessel dropped on a container filled with sulfur hexafluoride

Also, when we pour this gas over the burning candles, the heavy gas will precipitate on the candle, depriving the fire of oxygen and extinguishing it.

Is It Only Used For Fun Experiments?

No. It is an ideal gas for many areas, thanks to its properties such as high stability, density, non-flammability, and high molecular size.

  • SF6 gas is widely used in medium and high-voltage circuit breakers and electrical switches. Here, it acts as an arc extinguisher and provides insulation.

  • Due to its high molecular size and density, SF6 is also used as a cauterizing gas in many industries. It can be preferred in producing many high-tech systems, such as the manufacturing of semiconductor devices, photovoltaic panels, and micro-electro-mechanical systems.

  • If you had an eye operation such as retinal surgery or perhaps cataract surgery, there is a possibility that SF 6 gas has been injected into your eye. Because the surgeons use SF6 to fill the gap of the vitreous gel they removed to reach the retina. For this reason, especially after retinal surgery, traveling to high altitudes or air travel is prohibited until your eye doctor says that the gas bubble has disappeared from your eye (approximately 3-4 weeks). SF6 gas injected into the eye can expand at altitudes reached in an airplane and seriously damage the surrounding eye tissue.

  • SF6 can also be used to isolate accelerator tanks in particle accelerators.

Gas Used for a period in the “Air” Part of Nike Air Shoes

  • You must have seen Nike Air shoes, maybe even used them. If we went to the late 90s, sulfur hexafluoride would be the gas in the “air” part of these shoes. Since SF6 gas is not flammable and its molecules are pretty large, it could remain stable in the shoe for a very long time. It was an excellent choice for those times. However, when it was learned that the greenhouse gas effect of SF6 was too significant, Nike gave up this choice. The current Nike Air shoes mostly use nitrogen, another stable gas.
  • Some double-glazed windows use a gas mixture of SFmixture and argon to fill the space between the glass panes. It absorbs acoustic waves and reduces the noise coming from outside the window. However, due to the mixing of SFinto the air during the production of these glasses, the use of SF6 in the production of soundproof windows has been phased out or is being phased out in many countries.
  • It acts as a cover or protector in the production of magnesium. Thus, it helps prevent magnesium from reacting with oxygen.


Fun But Environmentally Harmful

The SF6 has a remarkable charm but has a flaw and a greenhouse gas effect. The greenhouse effect of this gas is 23,500 times greater than CO2(22,800 or 23,900, according to some sources), but it is present in the atmosphere at relatively lower concentrations. Because it has such high damaging power, SF6  is the most potent greenhouse gas, according to the Intergovernmental Panel on Climate Change. Although it is emitted in low amounts compared to carbon dioxide, it has an atmospheric life span of 3,200 years due to its high stability. As the gas is released, it accumulates in the atmosphere in an undisturbed state for centuries. Therefore, a relatively small amount of SF6 can have a significant impact on global climate change.

sf6 sulfur

References and Further Reading

DILO Company, Inc. (2022, May 25). 7 common uses of sulfur hexafluoride (SF6 gas): Dilo Company, Inc.. DILO Company, Inc. Retrieved February 1, 2023, from

Environmental Protection Agency. (n.d.). Sulfur Hexafluoride (SF6) Basics. EPA. Retrieved February 1, 2023, from

Helmenstine, A. M. (2019, August 9). Fun chemistry demonstrations with sulfur hexafluoride, the anti-helium. ThoughtCo. Retrieved February 1, 2023, from

Starr, M. (2018, July 23). Here’s why extinguishing candles with this gas is a monumentally bad idea. ScienceAlert. Retrieved February 1, 2023, from

Wikimedia Foundation. (2023, January 29). Sulfur hexafluoride. Wikipedia. Retrieved February 1, 2023, from

Asu Pelin Akköse and Mete Esencan have done the proofreading.

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Mete Esencan

Hello everyone! I'm Mete Esencan. I am a graduate student in the Department of Chemistry at METU. I was planning to establish a platform by combining the research knowledge I gained during my basic science education and the management experience I gained in the METU Chemistry Society, which I was in charge of for three years. For this purpose, in February of 2021, I took the first step and established the OkButWhy, a platform where we can write articles as if to chat about science, art and philosophy. I wish everyone a pleasant reading!

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