This very topic was the subject of today's Quilting Newsletter. You can sign up to get these with the link at the very top of the page... For those of you who didn't see it, this is what it said:
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Pre-washing fabric
There is quite a lot of discussion in the quilting community concerning pre-washing fabric or not pre-washing fabric. Many quilters are certain there is no need to pre-wash fabric and as many quilters insist that fabric must be pre-washed.
I pre-wash all fabric, backing, cotton batting, and flannel before cutting. I will list some of the reasons I pre-wash my fabric.
1.Pre-washing removes sizing and other chemicals left in the fabric during manufacturer. Some may have allergies to new fabric.
2.Pre-washing shrinks the fabric so the quilt won't shrink unevenly in later washings. Each fabric will shrink at a different rate and this could cause lumps and unevenness in the quilt. I have had first quality cotton fabric shrink as much as four inches in width!
3.Pre-washing insures colorfastness. If a fabric bleeds too much it can be treated with a salt or vinegar rinse or discarded before using it in a quilt. After a fabric is sewn in a quilt it can easily bleed onto other fabrics.
All of my new fabric is taken directly to the laundry room where I keep a small mat, ruler and pinking rotary cutter. I trim all the cut edges with a pinking rotary cutter. This helps alleviate the strings that hang from the fabric after it is washed and dried. When fabric is dry, I simply fold the fabric in my preferred method to fit my storage totes. I usually do not put the fabric away for several days to be certain the fabric is dry. I do not iron fabric until I am ready to use it. If I iron it first, and fold it for storage, it needs to be re-ironed again just before using anyway.
Flannel fabric will shrink even more than regular quilting cottons so it should be pre-washed. If flannel fabric becomes too soft from washing and drying, a light spray of spray sizing or spray starch when ironing would renew the body or stiffness of new fabric.
Cotton batting will shrink quite a lot and will give your quilt the "antique" look. If this is the look you wish to have, do not pre-shrink your cotton or cotton blend batting. If you don't want this shrinkage to occur, you would need to pre-shrink your cotton and blend battings. You do not need to preshrink 100% polyester batting.
Most brands of batting will have pre-shrinking instructions on the package. If not, simply fill your washing machine with warm water. Unroll and place cotton batting in water. Turn washing machine off and let the batting soak for at least thirty minutes. Do not agitate. Spin water out on a very short spin cycle and dry the batting in the dryer on low temperature.
Pre-shrinking fabric is a necessary and important step to quality quiltmaking. If you wish your quilt to be flat and smooth you don't want your fabric to be shrinking at uneven rates.
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Good article!