Abstract: A concrete form foam block, of an Insulating Concrete Form System, comprises a pair of opposed and parallel foam panels spaced using a plurality of plastic ties. Each tie comprises full panel height flanges which engage the panels and a web portion extending therebetween. The web comprises a plurality of horizontal members, preferably four or more, which are distributed substantially along the full height of the flanges. The web includes a pair of full height anti-flash members for preventing the escape of flash during formation of mould-in panels. The top edges and bottom edges of each panel are formed with longitudinal tongues and grooves which interlock with adjacent blocks. Preferably additional transverse top tongues and complementary bottom grooves are located at each tie, forcing the alignment of vertically adjacent block's flanges. The combination of full height and aligned flanges results in a substantially continuous flange for the attachment of finishing materials.