It has a fractal structure over at least 3 orders of magnitude, which contributes majorly to it’s incredible stability and low material density.
Find out more about the scientific background:
http://www2.cemr.wvu.edu/~ejb/web_res_grp/index_files/Page486.htm
http://eolus.phys.northwestern.edu/applied_physics/project-aerogel_simulations.shtml