A sash window or hung sash window is made of one or more movable panels, or sashes. The individual sashes are traditionally paned windows, but can now contain an individual sheet (or sheets, in the case of double glazing) of glass. To facilitate operation, the weight of the glazed panel is usually balanced by a heavy steel, lead, or cast-iron sash weight or counter-weight concealed within the window frame. The sash weight is connected to the window by a braided cotton sash cord, or a chain, that runs over a pulley at the top of the frame, although spring balances are sometimes used. Repairing a broken cord requires disassembling parts of the window frame.