I am fairly new to quilting, but have sewn clothes for years. I was always taught to prewash. I purchased a quilt kit. The fabrics were from the Fossil fern. I decided not to prewash. The pattern has 6 applique squares. I had to remake one square 3 times. The square shrank a full 1/2 in when I heat set the applique. At first I thought I had made an error in cuttng square. All fabrics were from the same line and this is the only one that shrank. I hope I am not disappointed with what the fabric does after quilted and laundered.