Bias tape is cut at a 45° angle to the selvedge and is therefore stretchy lengthwise. It's used for easily finishing fabric edges. Another special feature is that bias tape doesn't require seam allowances. It's sewn around your cut edges, so it doesn't change the dimensions of your sewing project.

Bias tape is cut at a 45° angle to the selvage and is therefore stretchable along its length. It serves for easy finishing of fabric edges. Another feature is that bias tape does not require seam allowances. It is sewn around your fabric edges, so it does not alter the dimensions of your sewing project.