Often, when I make or buy tea, I am annoyed by the fact that an air bubble inside the tea bag keeps the bag from sinking to the bottom of the mug. What I don’t understand is, although the air seems to be prevented from escaping, water easily enters the bag making the tea leaves wet, and the juices from the tea leaves easily flow into the surrounding water outside the tea bag. How does this happen? Presumably, the air molecules are much smaller than the complex organic tea flavor molecules and should pass through the bag much more easily.
WAG in progress: The water wets down the bag and helps seal it enough that the air can’t pass through? If you wet down a t-shirt and form a bubble with it in the kitchen sink, you can trap air that would otherwise pass through. My guess is that the wet tea bag is airproof just enough to keep the air from escaping at it’s current level of pressure.
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The phenomenon is not caused by the permeability of the air, but by the surface tension of the bubble itself. When the bubble is large enough that its diameter is greater than the lattice of the paper it is blocked by the coherence of the physical structure of the bubble. The water and tea are not physical structures, and pass freely through the paper.
Press the bag into a spoon before lowering it into the water. That should drive out the air before it becomes a bubble.
Tris
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Triskadecamus
The water and tea are not physical structures, and pass freely through the paper.
Surely you jest!
As you pour the water in the teabag is sealed by it before the air gets out.
My answer ,and it works for me, is to pour a little hot water into the cup first to warm it,tip that away, fill it boiling water again and steadily lower the teabag in.
If you put the teabag in very near boiling water the teabag floats up ,maybe steam bubbles form inside the bag and part inflates it.
Please report back on your experiments as this is a crucial matter to all us Brits 
Just poke it down to the bottom with a spoon and squeeze the bubbles out. Works like a charm.
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Joph, you’re absolutely right. It works in other ways too: When I took lifeguard and rescue training, one of the things taught to us was that if you found yourself accidentally dumped in deep water, you could make a pretty good flotation device from your blue jeans by taking them off, tying knots in the ends of the legs and blowing air into them.
Your brain-in-jar,
Myron
Imbibo, ergo sum.
Just pour the water first and then put the teabag in. That way the top of the teabag stays dry till all the air has escaped.
I agree “surface tention” is the key word here. The water-air surface acts like a rubber sheet, and it takes energy to break up a bubble into smaller bubbles.