the hair involved was typically horsehair from the main and tail. Long, fairly coarse, and stiff. I'm not familiar with any of the varieties Barb has talked about, but generally, horsehair canvas has had a spun fiber warp (the length wise direction), historically linen or cotton, but these days often something else (a synthetic blend, wool, etc). A single horse hair is used as each weft. Hair, being a protein fiber, is fairly non-stretchy. so the fabric has some stretch in the warp direction, but little along the weft. Hair, of course, also does a good job of shaping with steam and heat. (Think about curling irons...) Depending on how the horsehair is orientated in the clothing piece, you can achieve different effects. (I don't know how it's used in kilt making; i'm awaiting my copy of Barb's book...) For instance, in a (good quality, expensively made) suit coat, there is a piece of hair canvas in each front piece. The weft is arranged horizontally, so the jacket has stiffness from the buttons to the side seam, but is reasonably pliant vertically. A good tailor will put allowances in such that they minimize bulges, and make the coat hang right.

there are also hair canvases made of worsted goat hair, instead of single fiber horse hair. They're not as stiff (and, thinking about it, the only sort I've ever seen in a mainstream fabric shop, so might be what's being discussed now.)