TL;DR;
Nike used to put SF6, a greenhouse gas which causes 24300 times more warming than CO2 over 100 years, in the “air” cushions in their shoes. Nike stopped, and sold carbon offsets based on the counterfactual of what the world would be like if they kept putting it in shoes. These offsets are part of the “buffer pool” to compensate for the fact that some offsets turn out to be bogus or simply fail due to unanticipated consequences.
I have a pair of basketball shoes that have the Air technology. My other pair uses the more modern React cushion. Having said that, I’m never buying Nike again after a brief sneakerhead phase. I go for smaller orthopedic brands instead. They’re more comfortable too.
From the Wikipedia article:
Nike likewise used it to obtain a patent and to fill the cushion bags in all of their “Air”-branded shoes from 1992 to 2006.[36] 277 tons was used during the peak in 1997.[33]
I’m thinking about nitrogen, but I’m not sure if it stay in place for a few years.
I think that nitrogen is what they’re using now. It’s readily available, cheap, and fairly easily contained.
