Abstract: The invention relates to a formwork component for use in concrete construction for the formation of a recess in a wall or ceiling, the component comprising a hollow body defining a central axis, the body having a resilient wall and at least one spreader mechanism adapted to adjust the shape of the hollow body to vary its cross-sectional dimensions. In a first aspect the resilient wall includes at least one section bendable about an axis substantially co-planar with the central axis. The spreader mechanism may include at least one movable spreader component adapted to act on the resilient wall as a hinged lever.