Swimsuits made of nylon and spandex offer comfort and style. When the suit becomes faded or you want a new color, dye it at home with the right product. For nylon, that product is an acid dye, which is similar to a regular fabric dye but requires vinegar to set.
Fill a large pot with enough water to cover your swimsuit. Turn the stove on to medium heat and allow the water to heat until boiling.
Pour powdered acid dye into the pot. Stir the powder with a spoon until it has dissolved completely. Use the amount indicated on the box to get the shade that you want.
Run the swimsuit under warm water until it is soaked through. Place it into the pot and adjust the stove's temperature to just below boiling.
Stir the water continuously until it achieves a slight boil. Use a spoon to hold the swimsuit against one side of the pot. Pour a quarter cup of vinegar into the water, avoiding direct contact with the suit. Release the swimsuit and stir the vinegar into the water.
Reduce the temperature to medium heat and allow the suit to sit for half an hour while stirring occasionally. Medium heat provides enough heat for the acidity to affect the dye without damaging the spandex content of the suit.
Turn off the stove and remove the swimsuit. Wash it in a washing machine on the delicate setting with color-safe detergent to remove excess dye. Wash it alone to avoid damaging other clothing, and hang the suit to dry.