Some of Jacob Davis’s early riveted trousers used cotton duck before denim became standard.
Cotton duck is a tightly woven, durable cotton fabric. Davis used sturdy materials for work trousers made for laborers, and surviving historical accounts describe both duck and denim among the fabrics associated with early riveted garments. Denim eventually became the material most strongly identified with blue jeans.
The word “duck” in this context does not refer to an animal-based textile. It describes a heavy cotton fabric with a firm plain weave. Denim, by contrast, is a twill fabric whose diagonal rib is created by the way warp and weft yarns interlace.
Modern jeans are overwhelmingly associated with indigo-dyed denim, but the original patented concept was about reinforcement rather than a particular color or fabric. Copper rivets made the trousers more durable at points that commonly tore.