Read the label on your acrylic sweater. Most acrylic sweaters can be machine washed because they maintain their shape well. Be sure to pre-treat any stains on the sweater before putting it in the machine, and use a gentle cycle with the lowest possible water temperature. Try not to let sweaters go through the spin cycle. Stop the washing machine before the spin cycle starts, and gently remove the sweater. You can also use a mesh laundry bag to protect the sweater in the wash.
If you choose to wash your sweater by hand, use a gentle detergent intended for hand washing. Use the appropriate amount, as excess detergent is difficult to remove from sweaters. Use cool or lukewarm water. Don't scrub the sweater or try to wring it out.
Avoid putting sweaters in a clothes dryer. Instead, allow the sweater to air dry. First, place the sweater flat on a dry towel and firmly roll up the towel. Don't wring or twist the towel with the sweater inside. Then, place another dry towel on a large flat surface. Lay the sweater on top of the towel, and gently form it into its proper shape. Leave it to dry for 24 hours, then flip it onto a new towel and leave for another 24 hours. If you have a ventilated drying rack for sweaters, you can use that instead of a towel to allow the sweater to dry.