This sliding shade straps to your vehicle's sun visor. The shade extends to block the sun from your eyes when the visor is not long enough.
The "slide" part can be 3D-printed or milled from 6mm (1/4-inch) sheet stock. The "back" and "shade" parts can be cut with a laser cutter, water-jet cutter, milling machine, or even made with a band or jig saw and a drill. They should be made from from 3mm (1/8-inch) sheet stock, preferably dark-tinted translucent polycarbonate.
Assemble the slide to the back with 3mm (1/8-inch) pop rivets (8 of them). Gently flatten the backs of the rivets so that they don't rip the fabric or vinyl of your sun visor.
Slide the shade into the slot in the side.
Attach the sun shade to your sun visor with zip ties or any strap material up to 15mm (9/16-inch) wide. The straps pass through the slots in the corners of the assembly.
The zip file contains the parts, assembly, and drawings in native SolidWorks 2009 format.