Time to go sleep almost so shortly about my dreamed new material that is solid state but lighter then air though.
Made of carbon of course single or double atom walls create bubbles that in all create honeycomb structure.
Because in first grade there are empty inside ( absolute vacuum) total density is lower that air.
Due to carbon extreme qualities this sponge like material is not permissible to gases but solid like balsa wood.
Build of such material structure will be able to freely float in the air indefinitely long.
Depending on required altitude application ie 10 - 20 -50 km above the ground that individual bubble size could be bigger without compromising material stability due to low external pressure trying to squeeze our bubbles.
For surface landing crafts bubbles are build perforated and consist hydrogen or helium inside - and internal bubble pressure could be equalized.
Archetype of this material already exist and is called airgel - but remind me primitive clay pot constructions rather then precision atom by atom made more my spatial crystal.
Obvious application will be permanent flying objects but also perfect insulation material.
Physical properties will be determined by bubble size , thickness of carbon walls and internal content.
Since material should be also electric conductor future electronic application should be interesting ie quantum computing since material is both conductor and transparent to light. That allow to build interesting 3 dimensional structures trapping quantum inside.