These blanks are hand made in Australia and can be chambered before or during or after shaping.
The quality of balsa is so light - only 100kg/m3 that chambering is not required. Not like paulownia which is over 200kg/3.
So if we can build a solid balsa 9 foot longboard out of balsa it could weigh 9kgs - imagine the weight if built by paulownia? And if you hollowed it out you might be lucky to knock off maybe 2 kgs, and then risk the factors of shaping through the blank or it delaminated , having to put a vent in it and all those things associated with hollow boards.