Mat border widths change in popularity like fashion trends. The current style is the use of wider borders than the typical borders used decades ago. Today most people look at mats as an opportunity to add an accent to the frame design, but originally mats were neutral in color and used to give the viewer's eye space between the art and where it's being displayed. The wider the mat's borders the easier it is to focus on the art. Take your time experimenting with different options. They're endless!