No, not the buoyant waterfowl, the fabric.
Duck is a heavyweight basket-woven cotton fabric. If it’s not cotton, it shouldn’t be called duck. It’s sometimes called duck canvas or cotton duck. You will sometimes find it in a twill weave but the purists tell me that true duck is a plain basket weave.
It can have a stiff hand, but will soften considerably when washed. But it’ll still be a heavy ol’ thing and it suited for heavier projects. This stuff is GREAT for corsets. Corsets and tents.
Wikipedia tells me that there is a numeric grading system for indicating just how heavy a particular piece of duck fabric is. The scale runs from the heaviest weight at number one – think tents and sandbags – to the lightest weight at number 12, which is slightly less than half the weight of #1 and suitable for clothing. I must admit, I’ve never seen this grading system in use at a regular fabric store, but I suppose you might see it online.
Because it’s pure cotton, you absolutely MUST remember to pre-wash the fabric before you cut it for a project. This stuff can and will shrink by a significant amount. Cotton duck can go into the dryer – more shrinkage! – or line dry. Buy an extra quarter yard for every two yards needed for your project to allow for that shrinkage. Voice of experience, here.
Some ducks will fray with handling. Cut with pinking shears if you’re having that problem, or check the fraying with a zig-zag stitch along the cut edge, or use “Fray Check”.
An advantage of pure cotton and a heavier weight: It can take a hot iron and a lot of steam. You can do a lot with this fabric, once you’re used to it.
If you’re using a heavier-weight of duck, you might want to consider using upholstery thread, and use a needle that’s up to the challenge, as well. Lengthen the stitch on your sewing machine for heavy ducks, but if you’re sewing a corset, the default length should do you just fine. Use a roller foot for heavier weight fabrics and grade your seams to reduce bulk.