A method of forming a 3D mirror for a heads-up display (HUD) system includes providing a glass-based preform having a first major surface, a second major surface, and a minor surface connecting the first and second major surfaces, and further includes disposing the glass-based preform on a mold having a concave surface such that the first and second longitudinal side surfaces are adjacent to a longitudinal wall of a housing. The longitudinal wall extends from the concave surface to at least a height of the second major surface of the glass-based preform. The method further includes supplying a vacuum and conforming the second major surface to the concave surface of the mold using the vacuum. The first and second transverse side surfaces have a curved shape corresponding to a curve of the concave surface a remain coincident with the concave surface during the conforming of the second major surface.