This enlarged Aquabird has a foam core 90mm thick at the centre and is fully 3/4 Oz cloth covered. It also has a reinforcing bandage along the centre line and a vertical 1/8"plywood main spar.
I would say it is extremely strong. It has certainly enured its fair share of imperfect alightings, and also the odd landing on the bank.
I have managed to damage a float or sponson doing crazy things, but never weakened the wing.
Tough as nails