Full canvas structure is by far the best way that you can have your suit or jacket done with. This means that the front of the jacket constructed with a layer of canvassing that is attached to the front panel of the suit by stitching. The canvas gives the garment soft but firm support, which will last practically for ever. At least as long as the suit itself.
Canvas is made of horce hair and wool or cotton. In a jacket one is not able to see the canvasing, since it is situated between the suit fabric itself and the lining of the suit. Do ask your tailor if he/she can show you a piece of canvas. Once you feel, you will understand how it works.
And after all the best thing is that a suit made with fully canvased structure will get better and better over time. A bit like a high quality shoes adapt the shape of your feet, a full canvas suit will mold to follow the shape of your figure.
On the picture above you can see three different kinds of canvas. On the left is a light version of wool canvas. This is very popular nowadays, since vast majority of customers tend to prefer lightnes and "easiness". In the middle there is the standard woolen canvas for the more traditional structure and weight. And on the right you can see haircloth that has real horse tail hair strands in it. These you can see more closely on the picture below. The strands are peeking out from the edge of the canvas. When constructing a canvas for a suit, these strands will be secured with a additional layer of felt or other materila. This way they will not disturb the wearer by poking through the suit.