Most rayon garments are labelled dry clean only. It typically shrinks if it is machine washed, unless it is part of a blended fabric in which the rayon makes up less than 30 percent. There are also rayon fabrics that have been treated with special finishes to make them washable, but since machine washing greatly weakens the fibers even in treated rayon, its life is shortened.
If you mean a polyester spandex, to shrink it, you must wash polyester spandex in the hot water. It requires temperatures over 180 degrees Fahrenheit, make sure that you place your polyester spandex clothing in your washing machine on the smallest water level setting and choose the hottest water option.
Straightaway after draining the hot water out of your polyester spandex garment, put it inside a large pillow case and tie a knot at the end of the case (or lock the end with a rubber band). This will make sure that as you shrink your polyester spandex garment it will stay clustered together rather than be tossed and stretched as it spins in the dryer.
To shrink polyester spandex successfully, maximize exposure to dry heat by keeping the garment in the dryer ten minutes after it is fully dry.
Check out Clothing and Fabric Care Tips, shared by The Drycleaning and Laundry Institute.