As previously indicated, the original size of the sweater you purchased is not the actual size of the wool fibers. If you stretch it out again, you will be overstretching the strands and enabling them to shrink once again. Therefore, the only way to avoid another size increase is to get back into your old sweater and allow it to shrink down to a comfortable fit. Wool can shrink up to 20 percent of its original weight when washed properly. The amount that it shrinks depends on the quality of the wool and the method used for cleaning it. There are two ways to clean wool: dry-clean only or wash with water and soap. Shrinking happens when you wash wool in hot water with any kind of detergent. The higher the percentage of wool in the garment, the more it will shrink. You should wash new wool garments in cold water with mild detergents. Use color-safe chemicals and follow all instructions on the label. Rinse the item in cold water until the washwater is clear, then hang it up to dry away from direct sunlight. Wool fabric may also shrink when ironed. Follow all instructions on the manufacturer's label when washing and drying your piece of clothing so it doesn't shrink further when put through another wash cycle.