If you are purchasing or build a projector screen you should understand that an important element of any projector screen is a black border surrounding the screen. While it may seem like such a small thing this can have a dramatic effect on the quality of an image. Especially if you are projecting a high-definition image as most newer high definition projectors can provide a high level of brightness.
What material should the border be made from?
The first thing to look for with a black border is that it is made from fabric surrounding the screen, typically made from velvet, especially if you are creating the screen yourself. Some borders are made from metal, which tends to be thin, and can reflect light so you end up not receiving the image enhancement effects of a quality border. There are also some special fabric tapes which can be purchased for use with painted screens. If you are looking for the best possible picture be sure to look for black fabric on all borders, certainly if you are painting a projector screen you do not want to simply paint on a border, unless it is especially made for that purpose or things may end up looking worse than do without a border at all.
How does a black border enhance the image?
One of the things that a black border does is increase the brightness of an image. This occurs because the difference in brightness between the image and the border causes the brain to perceive the image as brighter. This is a very noticeable effect. Something you need to understand is that while this may only be a perceived improvement as someone who has created a projector screen I can tell you that the image projected without a border can look considerably more washed out. This really is not suitable in any sort of home theater.
Another thing that a black border does is absorb excess light on the edge of an image. This makes the overall image seen more even, and can compensate for slightly imperfect projector settings. The edge of a projector image can be very noticeable, and the way light is absorbed on the edge of an image can really help with the overall immersion in your home theater. Having a dark edge absorb this light improves immersion by making the edge less noticeable, this is another reason why you want to use fabric such as velvet for the border.