Sweatshirts can shrink due to heat and improper washing, but parents may also try to extend the length of a sweatshirt for a child who gains height but not girth. Stretching the length of a shirt while not expanding the girth takes time and patience. Fortunately, the process does not cost much money, because you likely have the household supplies necessary to complete the project.
Stop up a sink basin and fill it with water. Place the sweatshirt in the water until thoroughly soaked, a process which usually takes five minutes or less depending upon the type and density of the fabric. Soak the sweatshirt in a mixture of 1 tablespoon hair conditioner or baby shampoo per 1/2 gallon of water for better results.
Remove the sweatshirt from your sink and wring most of the water from it. Lay the clothing flat on an ironing board with the arms hanging over the sides of the board.
Turn on the steam setting of your iron and allow the iron to heat up for a few minutes before proceeding. Run the iron down the length of the shirt starting from just below the armhole and working your way down to the base of the sweatshirt. Take care not to stretch the armholes while ironing, or the sweatshirt will not fit properly.
Work in even rows vertically down the sweatshirt when ironing. Ironing from side to side will widen clothing instead of lengthening it. Repeat this process until the shirt has dried almost all the way.
Place the sweatshirt on a flat surface. Put a heavy weight, such as a dumbbell, on the shirt just below the armholes. Then stretch the sweatshirt slightly and apply another weight at the base of the shirt. Let the clothing dry fully before removing the weights.
If your sweatshirt does not have sufficient length after you complete the process the first time, repeat the process as needed until you achieve the desired length. Keep in mind that you can only extend the length of clothing so far beyond its original form with the total possible extension dependent upon the knit and material of the fabric.
You can more easily stretch sweatshirts made out of materials with a looser weave, such as cotton and cashmere, and you may experience poorer results with synthetic materials, such as polyester, rayon and silk.
You should not attempt to lengthen a sweatshirt by pulling on it with your hands, because you will stretch out the armholes, resulting in a poor fit. In addition, such a technique will not stretch the sweatshirt evenly, causing one side to sag more than the other.