There are the following types of binding cardboard:

(1) Gray cardboard. Also known as the bookcase cardboard, it is the national industry-specific cardboard for bookcases.

(2) grass cardboard. Also known as horse dung paperboard, the surface is rough and yellow. The cardboard of China's early book cover.

(3) Yellow cardboard. A surface that is smoke-yellow (same as kraft paper, which is smooth, rigid, and rigid, is commonly used for making bookbinding envelopes and for making book covers.

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