The support specifies whether an artwork is made on canvas, board, paper, objects, or other materials. It also specifies other relevant features of such support.

Cotton duck, heavy duty I started using a heavier cotton duck canvas in 2009, and it has become my preferred support since. This heavier canvas is a ready primed, unstretched, 510gsm (15oz) premium cotton duck canvas by The Canvas Company (either made by them in, or imported from, Australia). I find that this canvas is not as smooth and "glossy" as the lighter canvas, nor it is "ready" for use straight away but requires a few more layers of gesso to improve its whiteness if I'm intended to leave white areas untouched, or to seal it better if I am using extensive washes. However, it is invaluable when coming to constant handling, mounting and dismounting it from the stretcher, storing and, definitely, for unstretched artwork.
Cotton duck, medium weight My first artworks on stretched canvas are typically made on light, ready stretched canvas, of the type you can buy on any art shop. From 2006 to 2009, I have used a light canvas which is, typically, a ready primed, ready stretched, 268gsm (8oz) premium cotton duck canvas imported by Das, although I have also used a ready primed, ready stretched, 170gsm (5oz) cotton canvas imported by Artworks. This lighter canvas is a bit on the light side, and I will try to avoid it in the future, especially the 170gsm one. However, the canvas offers a very polished surface ideal for details and fast work. It is also well primed and ready to use, and the white surface is ideal if it is going to be part of the artwork as such. I also like that it is mechanically stretched and keeps its tightness very well if left untouched on its stretcher. Thus, I may still use the 268gsm Das's canvas for particular artwork if I need any of its positive features.
Synthetic canvas, medium weight Also on the light end of the spectrum, and definitely on the experimental end, is a ready primed, ready stretched, 268gsm (8oz) synthetic fiber canvas imported by Phoenix. I have used the canvas on some small artwork, trying to explore whether the synthetic fiber (apparently all synthetic, not polycotton) may turn out to be a more durable support than cotton. So far, the artworks hold without problems, and the canvas has retained its tightness very well. Unfortunately, it is still a light canvas. But if I were to find some heavy duty synthetic fiber canvas, I may as well consider a switch from cotton to synthetic, as it promises to be resistant to several "threats", such as molds, humidity, insects, environmental and chemical damage, etc.