When you bring home shiny new fabric from the fabric store or an online shop, the fabric can quite literally be "shiny." The bolts of fabric are often treated with various chemicals to make the print seem brighter and shinier under the store's fluorescent lights. Think about grocery stores waxing the apples so they appear shinier (and fresher??). Doesn't a crisp yard of cotton look so lovely you just want to dive in and start your project as soon as you get home?
It is worth every bit of patience you have to pre-wash that fabric before you ever cut into it.
The residues on the fabric can dull your sewing machine needle prematurely. Unless you are working with organic fabric, there will be some level of treatment. (Note: if you are working with a specialty fabric like silk or leather--you can possibly skip this step, though I do recommend pre-cleaning the fabric the same way you intend to clean the finished product.)
The most important reason to pre-wash your fabric is to pre-shrink it. Wash it exactly as you intend to wash the item you are making. Follow the care instructions on the end of the bolt (write them down before you leave the store since that information doesn't appear on a fabric ticket or receipt). If you're making pajamas, wash and dry the yardage as you would the finished jammies. I tend to wash everything in cold water (hot can cause some colors to bleed, but I have a product recommendation for that on another day), and then throw it in a hot dryer. Fabric can shrink significantly! Let me show you.
A crisp one yard cut of cotton before washing. This should measure 44" wide by 36" long (the online store I ordered this rainbow polka dot from always cuts 37" for each yard ordered).
After washing--41" wide.
After washing--36" long.
This yard has lost 3 inches in one direction, and 1 inch in another!! Think if you had made a fitted blouse for yourself without pre-washing. After all the hard work you pour into sewing a fabulous addition to your wardrobe, it shrinks in the wash and then you can't wear it!
Some quilters believe strongly that if you use quality fabrics, you do not need to pre-wash. There is less shrinkage with high quality fabrics, that is true, and much more from say, a Calico from the wall at Joann Fabrics. Many quilting experts feel the slight shrinkage adds to the desired stippled effect that happens when you first wash a quilt. I don't have a lot of quilting experience, but I disagree. If I want a 90" wide quilt, I want a 90" wide quilt! When you talk about garments, pre-washing is an absolute must.
Save yourself some heartache. Wash, dry, and then iron your fabric before you ever cut into it for a project. I do this with all of the products in my shop, all the home decor and clothing items I make for my family, all my handbags, my toys...whether someone intends to machine wash them or not. It's worth the effort!
As co-owner of Stitchery in Portsmouth, RI, I teach sewing classes to children and adults. Welcome to my blog Dancing Threads RI.