I was in need of some 3/8 light med-light Balsa, I checked out one supplier, but the price for contest balsa was astronomical, but Balsa USA looked much more reasonable   I ordered some "hand-picked not weighed soft balsa " From Balsa USA.  The order had 10 sheets of 3/8x3x36, 9 of the sheets were 6.1 to just under 5 Lb/Cubic foot.  Two sheets of 1/2" one 6 and the other 4.8.  I Had a hard time believing that, but I checked my scale against some sheets I had weighed from other orders.  Whether this is normal or I just got lucky I do not know.