Look up toroidal vortices on u-tube. VERY interesting stuff.

It depends on what the bubble is formed in and of, and what causes the bubble to hold together long enough to be called a bubble. And there is the gas, if no other substance, that constitutes the bubble filler. Examples of both bubble composition and gas contained, there could be: soap bubbles, alcoholic bubbles, gastric bubbles, bubbles with no outer thin membrane type like under water (which can’t pop but can be shattered into smaller bubbles), or in glass, rock, etc., fart bubbles, etc.
Are bubbles air tight? Yes. Otherwise they would self-destruct. Asking this question is sort of like asking if a frog’s ass is watertight. To a large or small degree, it depends on your point-of-view.

@kritiper I’ve seen a bubble shrink and not pop. :/

@Ltryptophan Restore the conditions that existed when the bubble existed and it will exist again.
Your question was about HOW they exist, no mention was made of how long they might exist, or what changing conditions might apply.