A liner for a manhole cover is made up of stackable sections. Each stackable section is formed of a plurality (e.g. 4) pieces. Each piece comprises a first arm and a second arm which are substantially perpendicular to one another, the first arm being longer than the second arm, and both arms comprising connection means to allow the pieces to be connected together. The respective dimensions of the first arm and the second arm are chosen such that, when the piece is incorporated into a stackable section comprising three other corresponding pieces that are connected to each other in a sequence of a second arm of one piece connected to the first arm of an adjacent piece to form a quadrilateral stackable section, a further corresponding piece can fit within the stackable section along an axis substantially parallel to the longitudinal axis of the first arm. Further corresponding pieces can thus be arranged within a complete stackable section to maximize the number of pieces that can be transported in a given space.