I usually prewash cotton woven fabric in cold water and tumble dry low before I cut it. Prewashing fabric ensures that your fabric will not shrink after you wash the completed garment. It would be really awful to spend a lot of time cutting and sewing something only to have it shrink after your first wash. If you want your fabric to last longer, then don’t put it in the dryer. You’ll also be saving energy by line drying.
Sometimes I’d rather skip prewashing because I just want to start sewing. But I tell myself it’s better to prewash.
You can even prewash silk, as I learned from Steph at her 3 Hours Past blog here.
The only exception I make is wool, which I don’t typically prewash. However, I might consider dry cleaning it before cutting. For example, I decided to dry clean some wool crepe fabric because I’ve read that it shrinks.
You can certainly throw wool fabric in the washer. Then it’ll be machine washable when you’ve completed the garment. I wouldn’t put it in the dryer though. My guess is that it would shrink more in the dryer than in the washer.
If you have a more delicate wool or an expensive wool, you might not want to put it in the wash because you’ll be putting more stress on the fabric and the fabric may get worn out more quickly.
When you prewash your fabric, be sure to finish the cut edges by either pinking the edges or just sewing a zigzag stitch close to the edge.
This will prevent any unraveling of the fabric as it goes through the wash cycle. If you don’t do that, you’ll end up with a mess of tangled strings.
If you are washing a piece of fabric that’s more than two yards long, it’s a good idea to sew then ends together in one big loop. Then the fabric won’t get all tangled up with the other fabric you’re prewashing.
I forgot to do that when I did a load of prewashing earlier this month. I had two longer pieces of fabric – one was about three yards and the other four yards – that I was washing along with other cotton prints that were one or two yards each. So when I took the load out of the washer and the dryer, the longer yardage was all tangled up with the rest of the fabric (as you can see in the photo above).
If you are using fusible interfacing in a project that you intend to put in the wash after you’ve finished the garment , you may want to prewash it in the washer or soak it in hot tap water for 15 minutes and letting it air dry (as mentioned on Fabricland’s site here). I haven’t experienced interfacing shrinking but I have read about other people having problems, such as in this post here.
Do you prewash your fabric before you sew?