It's realtive for buildings. Air-tightness is measured in air changes/hour, which measures how many time per hour the internal air of a structure is completely replaced my external air. Normal construction has 3 ac/h, if it recall. I bet they're aiming for anything lower than 1 ac/h.

Oh. That's interesting. It would read much better if they specified the ac/h rating they are referring to. It would also provide some actual information rather than a statement that sounds insane.

I guess affordability is relative. Last I checked, air locks were pretty expensive.