There’s Horizontal and vertical polarization as well as circular polarization. In a simple explanation , think of horizontal as a fence with horizontal bars so that only the horizontal part of the photons pass thru. Now once those horizontal photons pass, they will meet surfaces, which will reflect back their light so your eyes can see it. However, in this experiment only the vertical photons will pass your windshield. Because polarization depends on the angle of incidence, you will get some of the horizontally polarized light back as vertically polarized light which will pass thru. The effect is psychedelic. I totally recommend you to try it. You need polarized glasses, a flashlight and a piece of polarized film to place on your flashlight. The colors and shapes come back to you without defined form or glimmers so stuff looks normal, but weird as heck.