Fillers comprising a composition in which 50 to 90 wt.% or iron oxides and 10 to 30 wt.% of silica are contained, at least 50 wt.% of the iron oxides being present in the form of iron oxide silicate, and the content of alkali metal oxides or alkaline earth metal oxides is 10 wt.% or less in total, are suitable as fillers for the fabrication of noise insulating materials. Noise insulating materials obtained by using said fillers are excellent in flexibility and processibility and moreover are large in surface density, thus exhibiting excellent noise insulating ability.