Grainline, selvedges, warp, weft and bias - some fabric basics

When sewing clothes using dressmaking patterns, you will come across the word 'grainline'. The grainline is a line or arrow printed on each pattern piece to indicate the direction of the fabric grain.

This is because fabric behaves differently when pulled along the different grain directions: the lengthwise grain is the most stable, the crosswise grain is slightly flexible and the bias is the most stretchy.

When you are ready to cut the pieces out the fabric, you usually have to line up and pin the pattern piece onto the fabric with that arrow parallel to the fabric’s lengthwise grain. The grain arrows on pattern pieces ensure that the garment you are making will sit on the body without warping, twisting or creating unwanted creases.

To work out in which direction the fabric’s lengthwise grain runs, it is useful to understand how fabric is constructed:

Fabric that is woven on a loom has two sets of threads that run perpendicular to one another. The vertical threads are fixed to the loom and are called ‘warp’ threads - they make up the lengthwise grain. The threads that are woven over and under those warp threads horizontally are called ‘weft’ - they make up the crosswise grain.

It's so easy to forget which one is which - warp or weft - so my mnemonic for this is to say:

"right to left creates the weft"

How can you identify the lengthwise grainline of a fabric piece?

You may wonder how you can tell which of the fabric's threads were once attached to the loom if you are looking at a strip of fabric you have bought. This is where selvedges come in:

The lengthwise grain of a fabric always runs parallel to the selvedges.

Selvedges are created when the weft thread loops around the warp thread at the left or right edge of the fabric every time a row of weaving is completed. This creates an edge that cannot unravel (a 'self-edge'). Note that machine made fabrics sometimes still have a fuzzy edge at the selvedges, but there is a distinct strip of very tightly woven fabric that keeps it from unravelling. The selvedge is also the part of the fabric that any of the manufacturers' details such as the fabric's name or number (selvedge ID) are printed on.

What if the selvedges have been cut off?

If you have a piece of fabric where the selvedges have been cut off, you have the following options to identify the lengthwise grain:

1. Pull the fabric horizontally and vertically - the warp threads are tighter than the weft threads, so you will feel less ‘give’ when pulling along the lengthwise grainline.

2. Rip the fabric (if you have enough) - tearing fabric along the crosswise grain is much easier than ripping along the lengthwise grain. If you struggle to rip the fabric, you know it's the lengthwise grain.

What is the bias?

Some dress patterns require you to cut a piece of fabric 'on the bias', for example dresses and skirts that stretch or drape over the body, or when making 'bias tape'. The bias of a fabric is the 45 degree diagonal between the weft and the warp, where the fabric gives maximum stretch and flexibility.