A highly porous solid formed from a gel, such as silica gel, in which the liquid is replaced with a gas; frozen smoke: Aerogel is a highly porous solid formed by the replacement of liquid in a gel with a gas so that there is little shrinkage.

A gel formed by the dispersion of air in a solidified matrix like a solid foam, as Styrofoam.

Aerogel is a porous solid formed by replacing the liquid of a gel with a gas, such as rigid plastic foam.