Are aerogels an emerging noise control solution or it is just beefed up fiber glass?

Recently, there has been a number of publications which suggested that aerogels can offer high acoustical performance in terms of their ability to absorb or to insulate against sound. It seems that a bulk of these publications report laboratory experiments on the acoustical absorption or transmission loss performance for samples of particular thickness and lateral dimensions. None of these results appear to be rigorously linked to the aerogel's chemistry or micro-structure. This paper attempts to fill in this gap in information by explaining what these materials actually are, why they work acoustically and what is the underpinning physical phenomenon of aerogel. It is shown that the main reason that these materials are used in applications is that they are fire retardant or their elastic modulus is relatively independent of frequency and that they highly hydrophobic. It is also shown that the absorption performance of fibre glass impregnated by aerogel is generally controlled by the fibre diameter of fibreglass and by the density of the composite structure.