Hey Barry2067, that's a damn good question ,I wish i knew, must be genes got alot to do with it, I reckon if you dried them right.
Mine ain't all airy, just some, some hard as a rock, like the kind we grow outdoors, but I ain't been growing indoors to long, so I don't know wtf, is going on, with them buds sometimes.
Maybe some plant professor will see your post, an tell us all about it, but I can tell you our outdoor grows got dense, sticky, hard ass, buds. Can't say that about all my indoor grows though, but it still gets us high as hell, even being airy.