The really light stuff fits into my early rule of aerodynamics which is:
If th model is too heavy -the airfoil really does not matter
and
if it is light enough -it still does not matter.
When I got into the very small indoor flat foam aerobatic type models,I found that from a practical standpoint -you simply could not make the model too light - too flimsy but not too light.
these models fly in a no breeze enviroment
The avid contestants can do aerobatics which leave most wondering what happened to the laws of flight.
In scale - -the best still sems to be stick and really good Jap Tissue
most new flyers have no idea how this stuff even works
the one shown here, weighs a litte over 1/2 ounce