Everything You Need to Understand Fabric Grain and Grainlines

Fabric is made of fibers that are either woven or looped together. When the fabric is made of looped fibers it is called a knit fabric. When the fabric is straight fibers it is called a woven fabric. Fabric grain is the way the threads align with each other. Fabric has a lengthwise grain and a crosswise grain. Lengthwise grain runs the length of a piece of fabric and crosswise grain runs from selvage to selvage. To have perfectly straight grain the lengthwise and crosswise fibers run perfectly perpendicular to each other. Both knit and woven fabric have lengthwise and crosswise grainlines. Felt fabric and animal hides are two examples of a fabric that does not have a grainline.
Learning what makes up fabric helps you understand why fabric will hang in certain ways, how to use the grainlines that are printed on commercial patterns and why the fabric grain makes a difference.
Almost all clothing has a grainline that runs straight and perpendicular to the floor. The crease line on a pair of slacks is a straight grain line... or should I say... should be a straight grainline. If you've ever had a pair of jeans with one leg that wants to wrap around your leg instead of hanging straight down, you've experienced a garment that was not cut on the fabrics straight grainline.
Bias grain is the line that is at a right angle to the lengthwise and crosswise grain of the fabric as it is on the bolt. The bias has stretch even in woven fabric and will hang differently than a garment that has been cut on the straight or crosswise grain.
Almost everyone is familiar with weaving a loop potholder. These are a excellent way to learn how fabric is woven and actually seeing the way fibers are run to create fabric. The loops that are put in place would be the crosswise fibers. The loops that are hand woven to create the potholder would be the lengthwise fibers.