Abstract: a foldable backrest, including a backrest plate, operatively configured to be leaned upon by a back of a user. A support plate pivotally connected to the backrest plate operatively configured to be placed on a surface on which a user desires to sit or lay down on. One or more movable rigid wedges configured to form a desired angle between the backrest plate and the support plate in respect to the pivot connection between the backrest plate and the support plate. One or more wedge-stopping means for fixing the movable rigid wedge in a position for forming the desired angle. The one or more movable rigid wedge(s) configured to transfer mechanical support to the backrest plate from a surface on which support plate is positioned when the rigid wedge is fixed in a desired position by the wedge-stopping means.