Fabrics are woven with threads going in a crosswise and lengthwise direction. The threads cross at right angles - the more threads per inch, the stronger the fabric.
The crosswise threads, or grain, have a small amount of give to them; they will stretch a little. The lengthwise threads will not stretch at all. Cutting the fabric at a 45-degree angle to the crosswise and lengthwise threads produces a bias edge, which stretches a great deal when pulled (Figure 1).
Pay careful attention to the grain lines marked with arrows on the templates given with patterns, when marked. These arrows indicate that the piece should be placed on the lengthwise grain with the arrow running on one thread. Although it is not necessary to examine the fabric and find an exact thread to match, it is important to try to place the arrow with the lengthwise grain of the fabric (Figure 2).
Bias strips are used if stretch is needed, such as for binding curved edges, stems for flowers or some appliqué shapes.