 Until 2011, silica aerogel held 15 entries in "Guinness World Records" for material properties, including best insulator and lowest-density solid, though it was ousted from the latter title by the even lighter materials aerographite in 2012 and then aerographene in 2013.Carbon aerogels are composed of particles with sizes in the nanometer range, covalently bonded together.They have very high porosity (over 50%, with pore diameter under 100 nm) and surface areas ranging between 400–1,000 m2/g.