I think we all knew that BUT the latest research is that it’s not the vertical but the horizontal that we need to covet if we want to look leaner and taller. Peter Thompson, a perception specialist at York University, based his theory on much earlier work by the scientist Hermann von Helmholtz, who drew 2 squares, one with horizontal and the other with vertical stripes and compared them. The experiment showed that the one with horizontal stripes appeared taller and thinner than the other square. My own theory is that which ones work best for you depends on other factors. If you are very curvy, vertical stripes only highlight those curves, making you appear bigger, whereas horizontals will hug and enhance.  If you have no curves, the opposite happens. It also depends on the width of the stripes Very wide stripes can make you look bigger, whatever the direction of travel, or totally overwhelm if you are small in stature.