What is aerogel? Some know it as an excellent insulator. Some may know it as the “blue smoke” or “frozen smoke.”1 Although the record has recently been surpassed,2 some may still know it as the lightest solid (lowest density) from the Guinness World Records of 2002.3 Some think aerogel is made of silica but do not realize that silica aerogel is only one type of aerogel. As shown in one of the most recognizable pictures of aerogel (Figure 14.1), a silica aerogel against a dark background with a hint of blue and smoky texture is protecting a fresh žower from aburning žame due to its extremely low thermal conductivity.