Everyone knows that some fabrics, especially wool, which many sweaters are made from, shrink if washed at temperatures too high. See how to fix a shrunken item with a few simple tricks.
Soften shrunken wool fabric in a mild soap solution (or baby shampoo) for 10 minutes.
Put your sweater over a dry towel and pull the fibers, which have now been softened enough, until it returns to its original shape.
Leave the fabric to dry without pushing in any way or pulling too much the textile fibers.
For cashmere and wool, you can try a vinegar solution. Vinegar water percent should be a cup of vinegar to 2 cups of warm water, not cold, not hot. Leave to soak for about 25 minutes, then squeeze manually and pull the fibers to restore its original form. Leave wool sweater to dry and you’ll forget it ever came to shrink.
See below a tutorial with simple tricks to widen a wool sweater that has shrunk.