An expandable panel includes a generally planar panel portion, penetrated by several pluralities of spaced parallel cuts. The cuts include aligned sets of apertures and aligned sets of transverse gaps. The panel is expandable by pulling the sides apart, separating the panel along the cuts. The positioning of the apertures and gaps causes the panel portions defined between the parallel cuts to bend apart, defining front and back planes, to which sheathing, surface panels, or "skins," can be attached. The panel can be locked in its open position by inserting connectors in adjacent aligned gaps.