The standard sun visor in most cars are cumbersome and intrusive when used on the side window. I'm kind of tall so its right in (the side of) my face and blocks the rear view mirror. I can't see anything on my left side. My wife is petite so the standard visor doesn't always go down low enough for her. My Dad came up with this handy trick, which is to use a thin piece of plastic sheet. Just slip it between the window and the window seal. A round shape works best because it can be rolled into the best position as the sun shifts. The diameter I use is about 7-3/4". If the disc is too large it becomes obtrusive. The material is about 1/32" thick and made from HDPE - the same stuff those flexible plastic binders are made from. Mine was a pre-cut shape from Tap Plastics. When not in use it easily slips in the pocket in the door.