Border Edge Insulation with Skirt (8mm x 150mm). Border edge insulation or border edging is used within screeded floors and serves two main purposes. The first is to act as an insulation layer between the warm slab and the exterior walls of the building – it stops unnecessary heat loss from the slab at the edges of the room. The other purpose is to absorb any small amounts of expansion of the slab. It is typically installed at the same time as the floor insulation – it is either stapled to the wall or attached temporarily to the insulation panels, the screed finally holding it in place. Underfloor trade store also supplies a version with a ‘skirt’ – this is for flowing screeds to ensure that the screed doesn’t find its way down the edge of the insulation panels.