The present invention includes polymer interlayers that are used in multiple layer glazing panels. Interlayers of the present invention comprise a thermoplastic polymer, a plasticizer, and a fumed silica that has been modified to impart hydrophobic character. Interlayers incorporating such components have improved tensile modulus, moisture resistance, creep performance, anticorrosion effect, glass adhesion, and are well suited to a variety of applications, including, but not limited to, acoustic applications.