Provided is a novel foam composition for preparing polyisocyanurate foam. The composition comprises an isocyanate reactive compound, polyisocyanate, blowing agent and calcium carbonate filler component. The filler is loaded from 0.5 to 20 wt % based on the isocyanate reactive compound, preferably a polyol, and the average particle size of the filler ranges from 14.mu. to 40.mu.. The foam material prepared contains a high loading of filler, yet still exhibits excellent foam properties.