Production fabric is cut and sewn before it is washed and dried – meaning that the fabric is not pre-shrunk. This means that the shrinkage needs to be built into the pattern itself so that when the finished garment is washed and dried, it ends up at the measurements it is supposed to be.
So, when does that shrinkage get added to the pattern?
There are already so many variables that are tested when you fit a garment, so I prefer to keep shrinkage out of the equation until the end of development. However, I do test the fabric at the beginning so I know how much shrinkage we will be working with. With that knowledge, I create the pattern without shrinkage and fit that in an unwashed sample.
Once the sample is fit approved, I create a copy of the pattern and add in the percentage of width and length needed to account for the shrinkage. Having two patterns – one with shrinkage and one without – allows you to swap the fabric, add new colorways, or change the washing instructions later. Sometimes different colorways or a printed version of the same fabric shrink differently!
Adding shrinkage to the pattern at the end of development is the simplest time to add it in my experience.