About Fabric GrainThe term fabric grain refers to the way threads are arranged in a piece of fabric. Grain is one of those quilting topics that you might not think is important, but the way you cut your quilting patches in relation to the grain can produce quilt blocks that are accurate and easy to assemble--or blocks that just won't do what you want them to do.
Let's take a look at grain components.
Warp ThreadsLong threads, called warp threads, are stretched on the loom and secured. They become the fabric's lengthwise grain, the threads that are continuous along the length of your yardage as it comes off the bolt.
Weft ThreadsMore threads, called weft threads, are woven back and forth, perpendicular to the warp threads and along their entire length. These weft threads make up the fabric's crosswise grain.
Straight GrainThe lengthwise grain and crosswise grain are both regarded as straight grain, sometimes called straight-of-grain.
SelvagesSelvages are the bound edges that run along the outermost lengthwise grain. They are formed when the weft threads turn to change direction as the weaving process travels down the warp.
Fabrics are very tightly woven for a half-inch or so from the selvages inward, keeping the edges stable while fabric is on the bolt.
Fabric BiasTrue bias is defined as the direction at a 45-degree angle to the straight grains, but in quilting we refer to any cut that doesn't run along a straight grain as a bias cut.