When you’re developing a preliminary drawing for a composition, it often helps to refine it with layers of semi-transparent tracing paper. Architects use a cheap, pulp-based sketch paper that comes on a roll, available in white or canary.
It has been affectionately called “bumwad,” “fodder,” “tissue,” “trash,” "onion skin," “flimsy,” and “pattern paper.”
For the illustrator, it’s especially helpful for planning a group of overlapping figures, or for flopping a drawing. I know—you can do all this in Photoshop. But working out the drawing on paper is deliciously tactile, and just as fast.
Bienfang's line of bumwad: link.