Why It Matters
The fit of your finished costume depends, in significant part, on what's underneath it. A costume bodice fitted over the wrong bra will fit differently on the day when you're wearing a different one. A costume fitted without any bra will gap or pull when worn with one. Getting the foundation right at the start — wearing exactly what you'll wear under the costume for every fitting — is one of the most important and most overlooked aspects of costume construction.
Getting the Right Bra Size
Most people wear the wrong bra size. A professional bra fitting (available free at many lingerie retailers) reveals your correct size, which for most people differs from what they currently wear. For costume purposes, what matters is finding a bra that provides the support and shape your costume requires — whether that's a minimiser, a strapless, a long-line, or a custom-built internal structure in the costume itself.
Built-In Support
Many of Heidi's costume designs include built-in support — structured boning, internal corset elements, or foam padding — that eliminates the need for an external bra. This is particularly relevant for strapless or off-shoulder designs where an external bra would be visible. The Jessica Rabbit build is a good example: the internal structure provides genuine support independently of any undergarments.