Nike Air, the sneakers with cushioning support never relied on air for their "airbags". Instead sulfur hexafluoride gas (SF6) was used. Sulfur hexafluoride is a stable, dense gas (6.602 g/L; about five times denser than air).

Nike is currently phasing out the use of sulfur hexafluoride in their Nike Air cushions, because it is a serious greenhouse gas. In 2000, Nike used 200 000 lb of sulfur hexafluoride for their sneakers. The newer gas cushions will be filled with nitrogen.

Time to swap the old Nike SF6 sneakers for a green pair of Nike Nitrogen?

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