Learn about warp and weft in woven fabrics. The grain (or long grain or warp threads) is vertical, straight up and down, stable, and do not stretch. Crossgrain, (or width grain or weft threads), go horizontally across the fabric and have a little bit of stretch across piece of fabric. Bias grain is cut diagonally, so that the fabric can stretch and go around curves.

The grain runs the entire piece of the fabric. The grain runs the same direction as the selvage and the warp threads. The crossgrain (or cross grain) runs horizontally across the fabric, from one selvage to the other. The cross grain runs with the weft threads. The bias grain runs across the fabric, 45 degrees from the selvage, on the diagonal.

Fabric grains have implications for window treatments. Bias grains should be used for covering cording that goes around curves. For straight edges, such as on furniture bottoms, sometimes the cording cover is cut on the straight grain. If a bias cut is not possible, then the crossgrain (the grain across the width of the fabric) would be a better choice than cutting on the grain (down the length of the fabric). This is because the crossgrain will allow a tiny bit of stretch as the cording turns the corner of the furniture. True grains (down the length of the fabric) may be chosen to cover cording when there are no curves to go around and when it would be better to have one long continuous strip of fabric, without seams. Bias cuts are always preferred when cutting strips to cover cording, due to their ability to stretch and go smoothly around curves.