When washed in hot water, garments made of wool and cotton tend to shrink. But acrylic doesn’t respond to washing and drying temperatures the same way that natural fibers do. Instead of shrinking, the synthetic material actually stretches when facing high temperatures. Rather than trying to shrink an acrylic sweater, you may be better off exchanging it at the store for a smaller size or tailoring it to fit properly.

Prior to the early part of the 20th century, sweaters were made out of natural fibers such as wool or cotton. With the gradual introduction of synthetic fibers, such as acrylic, polyester and rayon, manufacturers began incorporating those materials into their garments. Some were 100 percent synthetic (such as acrylic), while others blended the fibers in different proportions (such as 60 percent acrylic and 40 percent wool) to create a specific feel.

Acrylic yarns were invented, in part, to avoid shrinking, as garments made out of natural fibers require special handling when laundering. Acrylic is also machine-washable and hypoallergenic, characteristics that differentiate the fabric from its natural-fiber counterparts. Also, the larvae of clothes moths are unable to digest the man-made fiber, so no holes.

On the minus side, acrylic knitwear is susceptible to stretching, notes garment analyst Dan Eisen in Treasure Coast News: “Acrylic yarn and fabrics are stabilized in manufacture by a heat-setting process, and when improperly stabilized, acrylic knitwear will stretch from the heat and tension in normal wear and in routine cleaning procedures.”

Guidelines on How to Wash Acrylic Garments

To keep your acrylic garment from losing its form and becoming baggy, follow the care instructions on the label of the piece you’re washing. Real Simple's Fabric Care 101 guide recommends washing man-made fibers such as acrylic, polyester, nylon and spandex in warm water and drying on a low setting or letting wet garments air dry. The guide also recommends using a fabric softener to help curb static.

While you may want to wash clothing made with natural materials every two to three uses, synthetic materials are more durable and can withstand four to five wears.

If you have an acrylic garment that you want made smaller, your best bet is to have it tailored; a professional tailor can customize the fit to your body. Alternatively, you might exchange the garment at the store where you purchased it. If all else fails, consider gifting the sweater or donating it to a good cause.