Abstract: A firestopping insulation construction adapted to be positioned adjacent to a head-of-wall area beneath a ceiling construction having fluted ceiling runner channels which have a trapezoidal cross-sectional profile facing downwardly. The insulation assembly includes an upper plug mated the shape of the fluted channel which is at least partially surrounded by an outer cover and further includes a lower insulation section extending over the side walls of the head-of-wall area. The upper insulation plug and the lower insulation sections are preferably made of molded high temperature insulation. The insulation assembly is engaged only frictionally to the fluted ceiling channels.