Usually, costume designers can apply modern conveniences to dresses and costumes that might otherwise be perfectly authentic for the Victorian era or some other historical period.
What’s most important is that the actors can get in and out of the costumes backstage in time to get changed and ready for their next scene. And thus it usually doesn’t matter what they’re wearing underneath.
But for the San Diego Repertory Theatre’s production of “In the Next Room,” the story dictates that some of the actors remove, and don again, their hefty dresses, petticoats, mackintoshes, stoles and bustles. And since they’re exposing what’s underneath in front of the audience, they must be wearing the official corsets and bloomers of the day.