While polyesters and synthetic fabrics don’t tend to shrink, natural fabrics like cotton and linen often shrink 3-5%. Depending on the tightness of fabric weave, shrinkage can be as high as 10%.
The greatest shrinkage for natural fabrics happens during the first wash and dry cycle. Lengthwise shrinkage is unrecoverable. Crosswise shrinkage may ease with wear – such as your favourite pair of jeans just out of the dryer.
By not pre-washing/shrinking your fabric before cutting/sewing, there is a very real risk of pulling your garment out of the washer/dryer and it is now one size smaller!
Another important reason is to wash out the dirt / remove chemical sizing / starch treatments / excess dye from the production process.
These processes make it easier for the manufacturers to handle the fabric during production, strengthen the yarn for weaving and allows for the end fabric to look great on bolt! Washing your fabric not only softens the fabric, but saves wear and tear on your tools – scissors, cutting blades, needles and excess dye/dirt debris on your sewing machine.
It’s best to wash and dry the fabric like you’ll wash and dry the final garment. If you plan on hand washing or machine washing/ drying your garment, pre-wash your fabric using that method.
When not to pre wash fabric?
100% synthetic fabrics do not need pre washing to prevent shrinkage, but it is still a good idea so you are working with a clean material.
For dry clean only textiles such as wool or knits, you can simply steam the fabric prior to cutting/sewing to help pre-shrink. Hover the iron above (not on! ) the fabric.
The exception to the pre-wash rule on natural fabrics might be raw indigo denim. Creases and folds from washing the fabric may lead to white lines on your fabric. It is possible to open up the fabric, lay flat in bathtub, shake it out so it’s smooth and then air dry as a single sheet – not folded.
Tips to Consider for Machine Pre-washing.
Unfold your fabric prior to putting it in the machine.
It’s best to wash the fabric on its own – not mixed in with other items.
Don’t overcrowd the washing machine and and don’t skimp on water. Overcrowding and insufficient water, particularly with natural fabrics can lead to some areas of the fabric not getting full water coverage and you will end up with streaks in your fabric that usually are permanent.
The excess dye will wash out and could stain other items in the wash.
Shake out the fabric prior to placing in dryer or hanging to dry. This ensures no permanent wrinkles or creases are created through the drying process.