Things You'll Need
String bikini top
Two large seashells
Purple paint (optional)
Hot glue gun
A seashell bra is a critical component of any mermaid costume. It can also be part of an outfit for a luau because of the beach theme of the seashells. Because real shells aren't very comfortable on their own and don't provide much support, your seashell bra will actually just be a decorated bikini top. Use white shells for a beachy feel or light purple shells if you are dressing up as Ariel from Disney's "The Little Mermaid."
Select a bikini top that you do not mind using for the costume bra. You will not be able to remove the seashells after you attach them.
Take the bikini top with you to a craft store and purchase two large seashells that cover most or all of the fabric on the front of the bikini. The seashells should be the scallop type and should be exactly the same size as one another. Choose shells with a coloring or pattern you like, unless you plan to paint them.
Paint the seashells light purple, if you would like your seashell bra to look like Ariel's in the Disney movie. Allow the paint to dry thoroughly before proceeding.
Turn the first seashell upside down and squeeze hot glue in a spiral -- starting at the center and going out until it is 2 to 3 inches in diameter. Do not go all the way to the edges of the shell, which might make the bikini top fit incorrectly.
Line up the bikini top over the seashell, and gently press it onto the hot glue. Be careful not to get any glue on your fingers.
Repeat the process with the second seashell, being careful to line up the shell in the same way so it will look even.
If the costume is for a child, consider making it more modest by having the child wear a flesh-colored shirt under the seashell bra.
Make fake seashells by cutting the shapes out of white or purple felt. Draw the scallop lines on them with a black permanent marker. Sew or glue them onto a bikini top to complete the costume.