If you look at the lego patent: http://npopson.com/images/legowallpaper/LEGO_WP_1920x1200_WHT.png http://npopson.com/images/legowallpaper/LEGO_WP_1920x1200_WH..

If you look at the lego patent: http://npopson.com/images/legowallpaper/LEGO_WP_1920x1200_WHT.png http://npopson.com/images/legowallpaper/LEGO_WP_1920x1200_WH... There's clearly not any air-tight seal. Most of the nubs on the top of pieces only have 3 or 4 points of contact with the piece they're connected to.