Why Clothes Shrink and How to Rescue a Shrunken Wool Sweater

The agony of popping a favorite wool sweater in the dryer only to find it's shrunk by one to five sizes is utterly frustrating. Unfortunately, the news is not good: most shrunken wool cannot be fully unshrunk. That's because wool shrinks not by dimensional change, like cotton, but through felting—when microscopic scales on the fabric interlock and irreversibly mat under the dual assault of heat and moisture.

Understanding fabric felting helps explain why wool behaves so differently. While cotton and synthetics typically relax or reshape when wet, wool can be permanently transformed by washing and drying together. The fiber's unique structure means that once the scales interlock, the damage is done.

If you are faced with a fresh casualty of the laundry, you can try a rescue attempt, though the outcome may be disappointing. Fill a sink or basin with cool water and a generous helping of hair conditioner. Submerge the sweater and gently work in the conditioner to untangle and enlarge the fibers. Once thoroughly soaked, carefully press out the water, avoiding twisting or wringing the sweater. Reshape it gently as best you can. Drape down on a towel to dry completely, smoothing it flat, reshaping it as far as it will go and letting it dry overnight.

While some felting may be undone this way, most damage is irreversible. After repeated exposure to laundry heat and moisture, wool is altered. Ordinary agitation matts microscopic scales, shrinking the fabric permanently.

Rinse thoroughly and press excess water from the garment. Do not wring wool. Reshape gently while damp and let the sweater dry completely, away from heat and humidity.

Know one boundary: you can't turn a shrunken adult sweater into a full-sized one again. But you may be able to extend the life of a wool garment that has shrunk down, or to freeze the felting at its current state, some of the damage can be mitigated. But altogether felting is irreversible once done.

Felted wool garments will continue to shrink, albeit more slowly. Even a small sweater may reduce by 10% or 50% its original size after repeated felting from washing and drying.

Perhaps disappointingly, the same variables that caused the felting are the ones you need to avoid next time. Heat, moisture, and agitation all contribute to felting. In general, avoid hot water when laundering wool, but in particular, never wash or dry your wool sweater using heat. Dry cleaning and cold water hand washing are the safest routes.

Overall, some shrinkage will always remain on the sweater. Do what you can to un-felt the garment as best you can, but live with it.

What's more, synthetics are different. Factors like high heat or polyester blending will affect garment size, but rarely in the way shrinkage does.

In summary, wool felting is not a pleasant experience. But it is an irreversible change in your wool once the fibers have interlock. There are ways to work with the sweater to get it to look like new as best as possible, but a fully restored sweater is unlikely in most cases.