If borders are used on a quilt's outer edges, binding width can be narrow or wide, depending on the look you're trying to achieve. But if the outer edge of the quilt is made up of quilt blocks, the finished binding width should be 1/4". Otherwise, you'll 'chop off' design elements in those outer blocks.
Quilt binding can be constructed from a fabric that's already been used in the design, or with any other fabric that works with the layout. Binding can be made from a single layer of fabric, but two layers (called doubleold binding) are much more durable.
Which Type of Quilt Binding Is Best?Lengthwise grain binding strips have threads that tend to run fairly straight along their length, ending up parallel to the edges of the quilt. If a single thread becomes weakened and breaks, it could split the binding along one entire side of the quilt, traveling as far as the weakened thread travels.
That scenario is most likely to be a problem for quilts that are used and laundered, both actions that allow the raw edges underneath the binding to rub against it abrasively.
Crosswise grain quilt binding strips are a very good choice. The grain isn't usually perfectly straight, so there's less risk that a split would damage an entire side -- it would be more likely to travel a short distance then stop when it butts into the quilt's front or back. Crosswise strips are also stretchy enough to wind around large curves along a quilt's exterior.
The grain in bias binding strips runs at more of an angle, so it moves from front to back after the binding is sewn to the quilt. A split would affect a fairly small area of the quilt's edge, giving you more time to make repairs.
Stretchy bias quilt binding is the best choice for quilts with tight curves and deep angles on their perimeter, but crosswise binding is perfectly fine for most quilts. I like to think of crosswise grain as a dual-duty method -- easy to sew and providing much the same results as bias binding strips.