The design of an arched window can add beauty and style to a room. Finding a way to cover up this design style with arched window treatments can create a challenge for any homeowner. Most decorators recommend leaving the arched section open and only add window treatments from the around the horizontal and below. If you find there is a need to cover the arched section, it is possible to have something custom-made for this section. To cover an arched window, either curtains or blinds will work. It only depends on the look you are looking to achieve in your room. To provide some privacy or filter light, you might try covering the arched section with a sheer fabric.