A folding frame wheelchair is a wheelchair whose frame is collapsible sideways by the use of an X mechanism in the frame. This mechanism is lockable, and the wheelchair folds on release of two locking levers on the chair. Because the folding wheelchair has an X mechanism, locking levers and re-enforcing struts, it is usually more heavy than a rigid frame wheelchair. Folding wheelchairs also have movable footrests which allow the chair to collapse. Early folding chairs were made from steel, but now days they are made from aluminium or titanium.