Originally Posted by
mjdarling47
Never mix pre-washed and unwashed fabric when making the quilt top as they will shrink differently when you wash the quilt and can cause puckering or bunching on the quilt.
Actually, mixing pre-washed and unwashed fabric in a quilt is not a problem as long as there is moderate quilting holding the three layers together. Quilting makes the three layers "one", with batting taking over control of shrinkage -- no fabric can shrink more than the batting.
Mixing pre-washed and unwashed fabric can be an issue for tied quilts and for quilts that are minimally quilted (say, in outlines of 12" blocks).
Fabric shrinks differently when washed and dried by itself (unpredictable) and after quilting (predictable based on batting). This is easily tested with flannel fabrics. Measure and cut 2 pieces. Wash one piece and measure it. Layer and quilt the other, then wash and measure. The fabric by itself will shrink more; the fabric in the quilt will not shrink more than the batting shrinks.