Polyurethane is a synthetic plastic material, widely used in creating pleather or faux leather. Should you discover a great pleather jacket second-hand or if you lost considerable weight, you may want to try and shrink the jacket if it doesn't fit properly. Fortunately, the material lends itself well to shrinking, but you have to take some precautions to do it right.
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Wash the jacket in your washing machine on warm to clean off the article. This helps prevent any contamination from "baking" into the plastic material in the dryer.
Slip the polyurethane jacket into an old pillowcase. Tie off the top with a shoelace to prevent it from falling out. Materials such as this might get hot enough to stick to the dryer's drum, damaging the jacket and making a mess.
Set the dryer on high. Let the cycle go for about an hour. Allow the jacket to cool off, then test fit. Repeat the cycle as needed, using progressively shorter drying times until the piece fits just right.