Pre-washing fabric: why, how and when to skip it

Yes, pre-wash almost every fabric before you cut it, and wash it exactly the way you will wash the finished garment. Natural fibers such as cotton, linen and viscose can shrink in the first wash, and strong dyes can bleed; it is far better for that to happen to a length of fabric than to a dress you spent a weekend on. Skip it only for fabrics that will never be washed, or that a wash would ruin.

Why pre-wash fabric before sewing?

• Shrinkage. Cotton, linen, viscose (rayon) and wool fibers relax and tighten when they are wet and heated. Most of that happens in the first one or two washes. A garment cut before shrinking can lose length and become tight across the hips.
• Finishes. New fabric is often treated with sizing or starch that makes it crisp on the bolt. Washing removes it, so what you cut is the fabric you will wear, with its real drape and handle.
• Dye. Reds, indigos and dark batiks can bleed. You want the excess dye gone before a white collar or a contrast pocket is sewn next to it.
• Mixed fabrics. A cotton outer with a polyester lining shrinks unevenly if neither is washed first, and the seams pucker after the first wash.

How much does fabric shrink?

It varies too much by weave, finish and mill to give one figure, so test your own fabric. Cut a 25 cm (10 in) square, mark its size with a permanent pen, wash and dry it as you plan to wash the garment, then measure again.

If the square comes back 24 cm (9 1/2 in) long, that is 4 % shrinkage: 8 cm (3 1/8 in) on 2 m (2 1/4 yd) of fabric. When you buy fabric before pre-washing it, add that margin to the quantity (see how much fabric do I need). As a rule of thumb, loosely woven linens, viscose, cotton gauze and flannel shrink more than tightly woven poplin or twill, and synthetics barely shrink at all.

How to pre-wash fabric, by fiber

The pressing column matches the dots on care labels: one dot is about 110 °C (230 °F), two dots 150 °C (300 °F), three dots 200 °C (390 °F). Blends follow the most delicate fiber they contain.

Step-by-step: pre-washing a length of fabric

1. Note the fiber and care. Take a photo of the bolt end or the shop's product page before you leave; you will not remember in two months.
2. Finish the cut ends. Zigzag, serge or pink the two cut edges, or sew a straight line 1 cm (3/8 in) from each. Loosely woven fabrics can lose several centimeters to fraying in one wash otherwise, and the threads tangle in the machine.
3. Wash it alone or with similar colors. Use the temperature and cycle you will use for the garment. Add a color-catcher sheet to dark or saturated fabrics the first time.
4. Dry it the same way as the garment. If the finished dress will go in the dryer, the fabric must go in now: drying shrinks fabric as much as washing does.
5. Straighten and press. Fold selvedge to selvedge and check the cut ends line up. Press with the right setting for the fiber, along the grain, before you lay out the pattern.
6. Label it. Pin a note saying "washed" and the date on the fabric if it goes back on the shelf.

Tip: Pre-wash the notions too. Cotton twill tape, cotton cord, cotton lace and cotton bias binding all shrink. Polyester zips and most elastics do not need it.

Pre-shrinking wool without washing it

Wool can felt in a washing machine. Most sewists pre-shrink it with steam instead: lay the fabric on the ironing board, hold the iron about 1 cm (3/8 in) above it on the wool setting, and steam the whole length without pressing down, letting each section dry flat before you move it. For a thorough job, roll the fabric in a damp sheet for a few hours, then unroll it and let it dry flat on a table. Washable wools (labeled machine washable or superwash) can go through a cool wool cycle like the finished garment.

When can you skip pre-washing?

• The finished item will never be washed. Wall hangings, some bags, a costume worn once.
• The fabric is dry-clean only and you will dry-clean the garment. Steam it well instead, since dry-cleaners steam too.
• Coated and special fabrics. Waxed cotton, oilcloth, laminated cotton, faux leather, many velvets and embellished fabrics. Washing removes the coating or crushes the pile.
• A toile in calico or muslin. A test garment only needs pressing. If you plan to wear it, wash it like a real garment.

What about interfacing?

Fusible interfacing should not go in the washing machine: the glue can come off. If you are unsure whether it shrinks, hold the steaming iron above it for a few seconds before fusing, then fuse with a press cloth. Sew-in interfacing can be soaked in warm water and dried flat like the fabric it supports. See interfacing for the different types.

Common mistakes and fixes

• Washing hot "to be safe". Hotter than the garment's care will over-shrink some fabrics and fade others, for no benefit. Use the temperature you will actually use.
• Skipping the dryer for a garment that will be tumble dried. It will shrink later, on your body. Dry the fabric the same way.
• A tangled, frayed mess after washing. Finish the cut ends first, and use a gentle cycle for long lengths.
• Fabric off grain after washing. Some fabrics come out skewed. Fold selvedge to selvedge; if the cut ends do not line up, pull firmly along the bias in the short direction, then press.
• Creases that will not press out. Take the fabric out of the machine promptly and press it while slightly damp.

Pre-washing is the first step in the sewing guide of every Sewly garment pattern, before printing and cutting, and it is the step people most often regret skipping. Once your fabric is clean, dry and pressed, you are ready to lay out and cut it on grain. For fiber-specific advice, see sewing with linen and sewing viscose without tears.