My research on two novels, one set in the 19th century, one in the 1920s, has led me to conclude that the greatest revolution of the late 20th century is in what women wore under their clothes. This may, of course, be connected to that other great revolution of the late 20th century, but it is certainly an overlooked one. In fact, one of the perils of research in this subject is that there are basically two kinds of books on the history of underwear. One is the slender kind, with lots of illustrations, usually written by someone who never paid much attention in college but who now writes for some recondite fashion magazine. In addition to the copious illustrations of women in garters and teddies, this kind of book will tell you what underthings Marie Antoinette, Lily Langtry, Mary Queen of Scots, etc wore, and will relay a few historical anecdotes which are now exploded and get a few names and dates wrong. Their version of history will begin with the Roman Empire. It is possible to pick up from a book like this bits of general information, such as when elastic was invented, and to get an idea of what an extremely chic character (should one ever stray into your novel) might have worn. It will tell you nothing about the average woman, however.
The other kind of history of underwear is usually written by a historian of women's studies. It will tell you about the genderization of underwear -- in other words, what men thought about women's underwear, and what women thought about women's underwear. (Nobody, to my knowledge, has ever written anything about what men think about their own underwear.) It will support its assertions by quoting the diary of a single crank who lived in 1820 and extrapolating this into a generalization that will fit all of 19th century society. What the average woman wore under her clothes will sometimes be mentioned, but only in very scattered instances, because it is not the function of such books to give practical information about average women's lives. This is serious history, and serious history is mostly about what people think about, and what they think about what they think about. It doesn't get any more solid than that.
Now, I'm being amusing here, but this is really serious. A girl in the 1920s wore, as near as I can figure, "step-ins" (what we call today "granny panties," and considered, in those days, highly erotic), if not longer underwear, garters, stockings held up by the latter, girdles, plus, at times, a belt contraption for sanitary napkins. You think walking around with all that under your clothes doesn't affect your character's state of mind? It is at this point that the historical novelist considers going downstairs and making one of those large, colorful icy drinks and maybe putting a little umbrella in it.
All I want is a good honest history about what the average woman might have worn underneath. I can skip reading another book about D-Day or the Tennis Match that Changed Life as We Know It or another biography of Jane Austen. Give me a historian who can write and point him or her towards the subject of women's underwear. Please.