Provided is a novel foam composition for preparing polyisocyanurate foam. The composition comprises an isocyanate reactive compound, polyisocyanate, blowing agent and mica filler component. The mica filler is loaded from 0.5 to 20 wt % based on the isocyanate reaction compound, preferably a polyol, and the average particle size of the filler is greater than 7.mu. but less than 11.mu.. The foam material prepared contains a high loading of filler, yet still exhibits excellent foam properties.