Why It Matters
The fit of a finished costume depends substantially 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 behave differently — sometimes dramatically — when worn with one. The foundation layer is where fitting begins.
Finding Your Correct Size
Most people wear the wrong bra size. The standard sizing advice taught in department stores has been widely shown to be inaccurate for many body types, and particularly for people with larger busts. A professional bra fitting — available free at specialist retailers — or self-measurement using current methods (measuring underbust for the band size, full bust to calculate cup size) typically reveals a size significantly different from what people have been wearing.
Take your measurements in the undergarments you plan to wear under your costume. Use those measurements to determine both your bra size and your costume measurements — they need to match.
Strapless and Backless Options
For strapless or backless costume designs, the options are: a quality strapless bra (look for boning in the cups and a silicone grip at the band — cheap strapless bras slide down), adhesive bras (limited support, appropriate for lighter-weight costumes), or built-in support structures in the costume itself.
Built-in Support
For custom or commissioned costumes, built-in support is often the best option for strapless and structured designs. This means boning channels sewn into the bodice lining, a built-in internal corset structure, or foam cups attached to the costume's interior. These structures provide support independently of external undergarments. See the Chimera Costumes guide for examples of bespoke built-in support in their commission work.
Testing Before the Convention
Wear the full combination — costume and undergarments — for a minimum of 2 hours before the convention. What feels fine at home for 30 minutes may become uncomfortable after 4 hours on a convention floor. Identify and fix any issues before the event, not during it.
Frequently Asked Questions
Wear your intended bra and take your costume measurements in that bra. If you change bra sizes between measuring and wearing the costume, the fit will change.
Depends on the costume. For most fitted bodices with full coverage: an underwire bra in your correct size. For structured or corset-based costumes: often no bra is needed if the costume provides built-in support.