Numbered ducks range from #1 to #12. The lower the number, the heavier it is. A #1 canvas is 27 oz per square yard and #12 is 11.5 oz.
Single fill ducks are generally lighter weight and more flexible, ranging from 7 oz to 12 oz.
If a canvas just has a weight and not a number, which means it’s a single fill duck. Single fill refers to the way it is woven.
The warp yarns run vertically and the weft yarn is woven between them, horizontally. Single fill ducks just have 1 weft yarn and numbered ducks have 2, making them stronger and stiffer.
Most canvas is left unbleached and undyed. It has a natural color and may have dark specs, which give natural canvas a characteristic rustic look.
Dyed Canvas comes in white and a variety of other colors from muted to bright.
You can also get primed canvas, which is natural canvas coated with acrylic gesso on one side. It is commonly used for painting on because it won’t absorb the paint like natural canvas will.