Also posted on AA, in response to the same question(s): I can tell you what I know, or think I know. First of all, I don't know what "hymo" is. And I'm not aware that there is a difference between horsehair and haircloth. Perhaps there is; I defer to a real tailor. A "structured" coat is typically made using several layers of different kinds of canvas or interlinings. The largest is a layer of wool/horsehair blend that is basically the same size as the front third or so of (each side of) the coat, running from the lapel through the chest, from the collar seam to almost the bottom edge. Then there is a piece of pure horsehair (much stiffer) in just the chest. The purpose of this is to smooth out and "clean up" the chest of the coat. Â Some add a piece of linen to the upper chest. The horsehair and linen are then covered with a light cotton flannel to prevent the horsehair from poking through the lining and scratching the wearer's body. These pieces are sewn together around the edges, and then padstitched with basting thread (white cotton) before they are put into the coat. This is what is meant by "making" the canvas. "Canvas" used in this sense refers to the whole internal structure. Once made, that structure is then pad-stitched to the coat front and lapels using colored silk thread. Â (Again, there are two of these structures, one for each side of the coat.) The problem with pre-assembled canvases is that they (obviously) come only in certain sizes. If a tailor has cut a unique pattern for a client, he can be pretty certain that no pre-made canvas will exactly match that pattern. So he has three choices: 1) Just put in the pre-made canvas anyway, which won't fit so well, and at best some of the fine effects of pattern cutting will be lost; at worst the shape of the coat will be seriously off; 2) Trim the edges of the canvas to make it fit better; this might work reasonably well, but it won't be as good as if the canvas were made according to his own pattern; and of course trimming is fine where the canvas is larger than the pattern, but what about those areas where it might be slightly smaller? And what if the canvas as a whole is the right size but (say) the horsehair piece really ought to be 3/4" forward and 1/2" down? Etc. 3) Take the canvas apart and remake it where necessary; this is generally so time-consuming that it obviates the benefits of a pre-assembled canvas, so the tailor just might as well make his own. Another issue is the materials used. Most of the really good tailors don't use the same exact canvas for every suit. They vary the materials according to the cloth they are working with. They generally have their own ideas about what works best with what. So for some cloths they will make a certain, stiffer assembly, for others they will do one that is softer. Sometimes they will use all four layers, other times they will use fewer, etc. With pre-assembled canvas, they are stuck with whatever is available. Okay. "Soft" tailoring does not use the whole assembly described above. The first thing to go is generally that pure horsehair panel in the chest. Hence, no clean chest but visible "breaks" or drape. Some love this, some hate it. Get rid of the scratchy horsehair, and you can get rid of the flannel which is there to protect the wearer from little stabs. At a minimum, this makes the coat lighter and bit cooler. Some go even further and use flax (linen) for the main interfacing, instead of the stiffer (and more common) wool/horsehair blend.