Fabric is constructed from interwoven threads. These threads are woven at right angles. The threads that run from selvage (the bound edge) to selvage are called the crosswise grain. The threads that run parallel to the selvage are called the lengthwise grain. The diagonal to the lengthwise and crosswise grains is called the bias. If you pull on the bias direction of a piece of fabric, it will stretch. If you pull on the crosswise grain, the fabric stretches only a little. If you pull on the lengthwise grain, the fabric does not stretch at all.If a block is constructed so that the outside edge patches are cut parallel to the crosswise or lengthwise grains, then it will tend to keep its shape, and not stretch out of shape.
This is also why sashings and borders are cut parallel to the lengthwise grain, even though this means purchasing more yardage. Not only does this avoid having to piece the sashing or borders to get the proper measurement, but sashings and borders cut this way are very stable. Distortion is avoided, and this helps the quilt remain square or rectangular.
Go to Using ARDCOTM Templates (A Pictorial Demo).
If you have any questions or comments on these tips, please send them to Shirley Templates, shirleyt@ardcotemplates.com.