Coutil is a strong cotton fabric made with a twill weave. It’s often confused with duck, or canvas, but duck is basket-weave and canvas is a balanced plain-weave. Coutil is usually made in solid black or white. If you know of a source of colored coutil, I’d love to add that to the resources page.
It’s specifically marketed to corset-makers as being especially tough, resistant to steels poking through and less likely to distort with wearing.
(I once had a terrible time when I made a corset with some duck that wasn’t up to the job and I swear, it stretched half an inch after I wore in the first time, from the pressure of the steels on the top and bottom of their channels.)
It’s heavy stuff, but up to the job of tight-lacing, if that’s what you want from your corset. It’ll cost you more than regular duck or ticking – about $20/yd in my experience – but it’s worth it. You can buy it from any place that sells corset supplies.
Despite manufacturers’ claims, you should wash your coutil in hot water and throw it in the dryer before cutting, just to be sure that it’s done all the shrinking it’s going to do.
Sew with cotton or all-purpose thread and a needle heavy enough for the weight of your coutil. If you’re making a corset, consider investing in a rolling foot for your machine so that it may better cope with bulky seams.
And while we’re on the subject of corsetry, visit FFC’s about making corsets page.