The invention is directed to a patterned aerogel-based layer that serves as a mold for at least part of a microelectromechanical feature. The density of an aerogel is less than that of typical materials used in MEMS fabrication, such as poly-silicon, silicon oxide, single-crystal silicon, metals, metal alloys, and the like. Therefore, one may form structural features in an aerogel-based layer at rates significantly higher than the rates at which structural features can be formed in denser materials. The invention further includes a method of patterning an aerogel-based layer to produce such an aerogel-based mold. The invention further includes a method of fabricating a microelectromechanical feature using an aerogel-based mold. This method includes depositing a dense material layer directly onto the outline of at least part of a microelectromechanical feature that has been formed in the aerogel-based layer.