Jim,

While I cannot prove them to be airtight. They have no hole in them. And the top & bottom do tightly fit together, just like a airtight. Try seperating the top and bottom. And you will see what I mean. I believe them to be aittight or at least be semilar or very close to a airtight if not a airtight.

There is NO case that is 100% airtight. And will stop completely the toning. But there are some that is much much better then the orginial caps. And these airtight caps will certainly slow down this toning.
Dan