Silk dupioni is plain-weave silk fabric with a distinctive “slubby” surface. Those slubs are from the silkworms’ cocoons, and they add a bumpy, almost rough texture to the fabric. In any other silk, these slubs would be a defect but, in this case, they’re a feature. I sometimes wonder if it was created as a marketing ploy by the silk industry.
(One of my reference books takes pain to point out that the silk thread used in this fabric is called doupion, to differentiate it from regular silk thread.)
Silk dupioni is usually light to mid-weight and it’s very crisp. Like taffeta (another crisp fabric) it rustles when it moves. It can be found in a range of solid colors, woven patterns and cross-weave (where the warp thread is a different color from the weft).
It’s often confused with silk shantung fabric, which is very similar. Dupioni has a rougher texture and more slubs than shantung.
It’s a great fabric for a lot of projects – from fantasy dresses and evening gowns to steampunk accents and various anime characters. And it’s relatively affordable. Lighter dupionis can be found for as little as $10/yd if you hunt around and hang on to your coupons. More typically, it starts at about $15/yd and can go ridiculously high because it’s silk and very popular.
It can be difficult to sew because it frays a lot and at the least provocation. Check out how to handle fray-happy fabrics to learn how to deal with that. It can be brittle and I’d be hesitant to use it for a corset, even flat-lined with coutil. If you want to use it for a corset, I’d pay the extra few dollars for thicker, heavier fabric.
Silk dupioni should go to a dry cleaner or if your costume can’t be trusted to one, hand-wash it in cool water and lay flat to dry.
If you like the look of silk dupioni, but can’t afford the price, there are lookalikes out there made of various artificial yarns. They’re warmer to wear than silk, but can be easier to take care of as well as being cheaper.

Polyester dupioni. Very tricky to tell the difference if a picture is all you have. Source: parameshwarweaves.com
Beware the seller offering silk dupioni at a price that’s too good to be true. Check the descriptive text for weasel words like silky or silk-like. Or the text might leave the word silk out entirely and count on the buyer making a (wrong) assumption. If you have your doubts about a fabric’s composition, get a swatch and perform a burn test.