Should you pre-wash fabric before sewing?

When starting a new sewing project, you’ll often find that the instructions you’re following tell you to prewash your fabric. We’ve all been there - staring at the fabric, wondering if prewashing really is necessary. Why wait for the washing machine, the drying, and the ironing process to be over with when you could just dive straight into your next project? 
 
As annoying as it is, pre-washing fabric is actually a vital step in most sewing projects. To learn why you should pre-wash your fabrics, how to wash them, and a few exceptions to the rules, keep on reading.
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Why you should pre-wash your fabric before sewing.

​Avoid shrinkage by pre-washing your fabric before sewing.
The main reason it’s advised that you prewash fabric before sewing is to avoid shrinkage. Seasoned sewists will tell you that most natural fibres shrink during their first wash - a fact they probably found out via the hard way!  Cotton shrinks by about 5% when washed for the first time, but it’s not uncommon for cotton and other natural fibres to shrink by up to 10%. 

Wash your fabric just like you’ll wash the final garment.
The old “measure twice, cut once” phrase won’t help you if your fabric shrinks when wet, so avoid this problem completely by washing your fabric before sewing. If you’re planning on hand washing the garment, you need to prewash the fabric in the same manner. This means that if you’re planning on making your garment machine washable, make sure the fabric has been pre-washed in the washing machine at 30°C. 
 
It’s also handy to throw your fabric in the tumble dryer too if that’s a method of drying you’re going to be using as part of your normal laundry routine. Even if you’re planning on air drying your garments, it’s good to put the fabric in the tumble dryer, just in case your garment ends up in there by accident.

Pre-washing also helps rid fabrics of dyes and chemicals.
Another great reason to pre-wash your fabric before sewing is to wash away any chemical treatments, dyes, starch, and dirt. A starch treatment is often used on the fabric to make it look crisp and clean on the bolt, so pre-washing the fabric makes it softer and easier to work with.

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When is it okay to not pre-wash fabric before sewing?

​There are a few cases where a pre-wash is not strictly required, although some preparation might help with the overall sewing process.
 
If the item you’re planning on sewing is unlikely to need washing - for example pencil cases, peg bags, scrunchies, bunting, and other accessories, then it’s not strictly necessary for you to pre-wash it. If it can be cleaned with a damp cloth effectively, there’s no need to wash the fabric before sewing.
 
Fabrics that are dry clean only and garments that need to hold their structure would benefit more from a light steaming before cutting and sewing. Hold an iron above, but not on, the fabric and let the steam penetrate the fabric, this method also allows for any fabric shrinkage. 
 
100% synthetic fabrics aren’t likely to need pre-washing to prevent shrinkage, however it’s still worth washing the fabric as this will remove dirt and dyes. 
 
Pre-washing denim may lead to white lines where the fabric creases and folds during the wash. For this reason, some people don’t pre-wash denim and prefer to cut and sew with it straight away.

How do I pre-wash my fabric?

We already spoke about how you need to pre-wash your fabric just like you’re going to wash the finished garment. 
 
One thing to consider is the raw frayed edges of the fabric. In some cases, you may need to protect the raw edges before pre-washing your fabric to avoid losing length. Pre-fraying your fabric is one option, or running a zig-zig stitch or overlocker up the raw edges is another method to prevent fraying.

Of course, you could always pre-wash your fabric and remove the frayed edges afterwards - but if you are planning on measuring the shrink rate - you will need to finish the edges first. and ALWAYS finish the edges on Sweater Knit fabrics as they will die a death in your machine without it. 
 
Looking for a few more tips on pre-washing fabric before sewing?

• Do a test wash first before washing the entire length of fabric - if you cut a 10cm square and wash it you can also calculate how much shrinkage there will be in your final garment and if it is necessary to pre-wash first
  
• Wash similar colours together
  
• Unfold the fabric before you wash it in the washing machine
  
• Do not put too much fabric in the washing machine at once and hang IMMEDIATELY to dry, as flat as possible and un gathered on the line.
  
• ​Be aware of distortion as you dry - so make sure the fabric weight is distributed evenly
  

If you have any questions about pre-washing hop on into my free Facebook group Kernow Sewcial to ask any questions - I'm very quick to comment or reply and there is a huge community of wonderful sewists just waiting there to support oyu as you go!