Fill the washing machine, the storage or bath tub, or other container with water. Cold water is best for this process.
Immerse the jersey in the water, letting it remain until thoroughly soaked and the fibers are loosened. This should take about about 10 minutes.
Remove the jersey from the water and ring it out by hand to remove much of the excess water. However, make sure it is still sopping wet. The more saturated the fibers, the easier it will be for the fabric to expand.
Place the bottom of the jersey around the back of the wide-backed chair and gently work it down over it until it's as far as it can go. It is important to do this gently so that the fabric only stretches and is not damaged by stretching it too fast.
Rotate the jersey around the chair back repeatedly and at regular intervals. This action should be continued until the jersey is dry. This is to ensure that even stretching occurs. You don't want the jersey to be bigger in the stomach but still too narrow at the sides, or vice versa.