"Balsa has been incorrectly considered to have the highest strength to weight ratios of any wood in the world.
Paulownia has been thoroughly tested and found to have a higher strength to weight ratio than Balsa!
Auburn University tested the strength of 18 lb p/cubic ft. Paulownia against Balsa, with an average weight of 10 lbs p/cubic foot."
Paulownia Trees: Fast Growing Royal Paulownia Tree vs Balsa Comparison 