If you have a trailer or some piece of equipment that sits a lot, accumulating enough inactivity to dry rot the tires off I have tried a little experiment. I was looking for something to fill tires other than air that might help them last longer. Supposedly the oxygen in air will permiate the rubber at a slow rate. Eating away at anything that will react with oxygen. I was able to identify 4 gases pretty early on that wouldn't cause immediate catastrophic failure. Nitrogen. People selling it claim that it violates ideal gas law. It makes up about 80% of the air. It's air with out the oxygen. Nothing special about it besides hype. Argon. An inert noble gas normally used as a welding shielding gas. Rumor is lexus would factory fill the tires with this substance to provide up to a 1db quieter ride. It's insulating properties make it less than ideal for a hard working wheel. CO2. jeep guys deflate their tires for better grip off road, then would fill their big oversized tires back up with CO2 after trail riding before they get on the highway. CO2 also has good heat conduction and inferred absorbing properties. Something called "stayfill". All I know is its not CO2, it's nonflameable, its held in liquid state at room temperature at a relatively low pressure. Given that plus the Montreal protocol it's very likely this product is R-125 (halon fire suppressant) or R-143 ("canned air" or computer duster). Helium. It conducts heat something like 6 times faster than air. Rumor is it leaks out a lot faster than air. Fact is its expensive and I have to send my helium tank off to get filled which takes weeks. Main use for helium is welding and balloons. Since I do a lot of welding I don't have to try and find helium, argon or CO2. I already have them. I also have the universal refrigeration license so I can buy refrigerants and work on pretty much everything but ammonia systems. I did some more reading and digging around to find out if maybe other refrigerants like the stayfill have desirable properties. R-125 fire suppressant conducts heat so well that even in gasous state it pulls heat out of burning materials almost like putting water on it. R-143 gas absorbs inferred radiation almost like a solid or liquid. Around that time I found a lawsuit involving McClarin motor sports and ferrari if I remember correctly. One of them had spent years and hundreds of thousands of dollars on finding the ultimate gas mixture to fill tires with to help the tires used in F1 racing run cooler and last longer. Then supposedly the other racing team just happened to invent this gas mixture over night. So they were being sued. After this tiff the finer points kind of the complaint spilled over into public domain. Oops. That super secret mix is a blend of R-404a and CO2. So you wouldn't just get the idea to suddenly start putting this exact gas mixture in a tire. R-404a is a blend made up almost entirely of R-125 and R-143 both are non flammable and stable to at least 400°F. So that's what I have been using for the last 3 or 4 years in trailer tires. I figure anything that doesn't contain oxygen is good for tires that won't be sitting and anything that doesn't insulate is good for hard working trailer tires. I don't figure there is any point putting this in daily driver tires because at least on my vehicles about the time the tires start weather cracking they're getting pretty low on tread and need to be replaced anyways. For a garage queen or maybe your hiden BOV just something oxygen free besides argon or helium (because remember the argon insulates and helium leaks out fast) The way I fill them is vacuum out the air with one of my HVAC vacuum pumps. Fill with CO2 and purge. If you don't have a vacuum pump just filling with CO2 and letting it out a few times will do the trick. I use the vacuum pump because I'm cheap and I have it, so might as well use it. Then use absolute pressure to obtain the desired mixture at the desired pressure. To fill something with R-404a you have to charge as a liquid since it's a blend. If you charge as a gas you get mostly R-125 or 143 which ever one has the lower boiling point. I do this by turning the tank up side down and just barely cracking the outlet valve open bumping the tire pressure up by 5psi or so at a time. The pressure goes up really fast dispensing liquid so be careful. Last time I filled the tires on my big trailer was 3 years ago and they are just now getting to where they need to be topped off again.