First ... did you try a 'search the boards'? There are hundreds of threads and posts on your query ... 😉
Now that I've gotten that of my chest ... I'll give you my thoughts (after all, it is getting close to Christmas:
The tubos are not air tight ... but because of the cork that is usually in the cap, they are very slow to humidify. Most will tell you to take the caps off, leave them in the tubes ... and place them in your humidor.
Most wooden humidors are not airtight. They are designed to breathe ... and it is a very necessary part of cigar aging and preservation. So, if you keep your cigars in an airtight container ... it is very important that you open it every so often to let the cigars breath, or they could develop mold, or could go sour on you.