Pre-washing fabric means washing and drying your fabric before cutting and sewing your garment.
For woven fabrics: Pre-washing is strongly recommended. Many woven fabrics shrink after the first wash. If you skip this step, your finished garment may shrink and no longer fit properly.
For stretch fabrics: Most polyester spandex and synthetic blends do not shrink much, but pre-washing is still recommended to remove factory chemicals and relax the fibers.
If your final garment will be machine washed, wash and dry your fabric the same way before sewing. This ensures the fabric behaves the same after construction.
For specialty fabrics like velvet, vinyl, faux leather, or metallic spandex, always check the care instructions first. Some materials should not be machine washed and may only need light steaming instead.
Pre-washing helps prevent shrinkage, dye bleeding, and unexpected changes in texture after your garment is finished.