Shrinking a pure cotton T-shirt is relatively easy. It seems that after each wash the shirt will get smaller and smaller, even if you don't try to shrink it. Shrinking a blended shirt is a bit different. Polyester is added to cotton so that it doesn't shrink much, and the higher the added polyester, the less the T-shirt is apt to shrink. Any T-shirt containing cotton will shrink a bit; the blend of other materials is the key to how much it will.
Things You'll Need
Washing machine
Dryer
Iron
Stove top with pot
Water
Pressure cooker
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Step 1
Wash the T-shirt in the hottest cycle that your washing machine allows.
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Step 2
Dry the T-shirt on the highest heat setting, then wash it again the same way.
Step 3
Pull it out of the washer and dry it by ironing the shirt with the iron on high.
Step 4
Boil the T-shirt on top of your stove in a suitable pot filled with water. If possible, put it in a pressure cooker instead, and allow the temperature to reach well past the boiling point of 212 degrees.
Step 5
Dry the shirt with the iron; it will have shrunk.
Warning
Boiling the T-shirt in a pot on the stove or putting the shirt in the pressure cooker might ruin it, so only use either of those ideas as a last resort. And be careful when using boiling water in either of these two applications to prevent scalding or burning your skin.