Do I need straight or bias binding?
To answer to that question, first determine how the quilt will be used. Is it a wall hanging? A table runner? Placemats? A baby quilt? A bed quilt? Will it be laundered often, or rarely?
Then ask yourself, “What is the binding’s function?” What I mean is, is it just a way to cover and protect the edges of the quilt? Will the fabric used for the binding simply need to blend in with the border fabric or will it serve as a decorative feature to frame the quilt?
The answers to these questions help to determine whether to use a binding that is made from bias strips or strips that have been cut from either the straight-of-grain or from the cross-grain.
Also, if your quilt has straight edges, you can choose to use either straight-grain, cross-grain, or bias strips for your binding. If, however, your quilt top has curves, you must use bias strips for the binding or it will not lay flat.
A bias binding is stronger because it has many crossed fibers on the edge. A straight binding only has a few. More fibers equals more strength.