I tried this with a wool sweater I bought at a garage sale. The problem was I have a new "energy efficient" washer. It never get hot enough to shrink the wool:-( The good news is my t-shirts and other clothes don't shrink in the wash either. A friend told me I could boil the sweater on the stove, but I need to keep stirring it because the motion helps the wool to shrink. One of these days I'm going to try it.