A tote bag side panel, a pocket, or a simple hem might get cut cleanly and look perfect, but after sewing, it could behave oddly in strange ways. One side might pull more than the other, a sewn piece may twist when finished, or the fabric could refuse to lie flat after you press it out. If the sewing machine, the thread, and the seam allowance are all okay, the one thing you might forget is fabric grain.
The term grain refers to which way the threads in a fabric are woven. In most cases, the lengthwise grain runs up-and-down through the fabric parallel to the selvage (the finished fabric edge). The crosswise grain runs left to right from selvage to selvage, while bias is at an angle across the fabric. These directions don’t react the same way. The lengthwise grain is generally less prone to stretching, the crosswise grain can have a tiny bit more “ease,” and bias has the capacity to stretch and warp the most.
For beginner sewing projects, grain is important because pattern pieces are designed for the piece to sit in a particular direction on your fabric. If a rectangle, a pouch piece, or even a garment piece isn’t cut perfectly on-grain, the seams can warp as the project takes shape. Even if you have a perfectly straight stitch and it looks okay on your sewing machine, once you turn, press, or wear it, the project may hang at a slight crooked angle. This can often become more obvious on hems, straps, facings, and large pieces of fabric.
Take one square scrap of fabric and test the difference yourself. Pull your fabric gently lengthwise along the selvage, then pull across from selvage to selvage, and finally try pulling diagonally from one corner to another. You’ll find that the diagonal pull usually has much more room for stretching. Also, try cutting two strips (perhaps inch-wide strips for this example): one strip cut on-grain (usually meaning along the lengthwise grain) and one cut on the bias. Machine-stitch a seam on each strip and then press them. When you hold the strip that was cut on bias it may feel more pliable, less stable, and that explains why cutting a piece off-grain by accident could affect your project.
Before you start cutting, make your fabric straight without stretching or distorting it. Find the selvage, make sure your fabric isn’t skewed, and then place your pattern piece so that the arrow on your grainline is aligned properly to the grain. Or, for a simple rectangle without a pattern piece, use a ruler against the selvage as your guide. With tailor’s chalk or a washable marking tool, mark your line before your fabric shears or rotary cutter ever touch the fabric. Skipping this can lead to complications which become harder to correct once your sewing begins.
Pinning or fabric clipping will also be easier once you ensure your fabric is lined up well beforehand. If one piece is just slightly crooked, your pin might just lock in the error instead of straightening it out. After cutting, place two matching pieces right side to right side and see if the raw edges are resting nicely without pulling. If you see curling, stretching or shifting in your fabric, stop before sewing. It may be possible that one piece is being cut on-bias, or that you accidentally stretched that piece when preparing it.
Before you start cutting each individual piece, ask yourself: “What is this piece meant to follow?” If you keep in mind which direction is which when you work with a project, your seams will be easier to handle, your hems will press better and your little sewing projects will maintain their original design with much less hassle.