Denim gets its blue from indigo-dyed warp. There are two main ways to dye that warp, and each shapes the fabric.
Rope dyeing
Warp yarns are grouped into rope-like bundles and dipped repeatedly in indigo, building deep, ring-dyed colour with a white core — prized for classic fades. Needs strong, even warp yarn.
Slasher (sheet) dyeing
Warp is dyed as an open sheet in one continuous line — efficient and common for volume denim, giving slightly different penetration and shade.
What it means for yarn
Both need robust ring-spun warp that survives dyeing and weaving; open-end yarn often fills the weft. See yarn for denim and open-end yarn.
Sourcing denim yarn? We supply indigo-ready warp and economical weft.
More in our yarn guides.