Mull is a net-like, woven linen or cotton fabric (linen is stronger than cotton) that's been treated with a starch to stiffen and strengthen it. Mull is also called "Super" and "Crash" and "Tarlatan". The mull is glued onto the spine of certain book structures to aid in strengthening the spine, and, when overlapping the spine, also helps strengthen the endpapers in the hinge part where they attach to the book board. If this doesn't make sense now, it will in future tutorials where we show it being used in constructing a book (see photo of spines with mull below). Mull can be substituted with natural, unbleached, undyed muslin.
Rice paper is very thin. Almost tissue paper thin. However, it's also extremely strong for how thin it is, and can be used the same way mull is, but on smaller or lighter books. Mull is thicker than rice paper, and we use it for heavier or larger books, but rice paper has been outstanding for 4" x 6" and smaller books. It's especially great for miniature books when the thicker mull would be too bulky.
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