100% cotton. 9m skein Weeks Dye Works threads are hand over-dyed. The company strives to offer the best color consistency in the industry but as there are no dye-lots thread skeins may show variations, and we cannot guarantee colour matching in an order. Note: This thread is NOT colorfast. Weeks Dye Works are transitioning to color-fast threads and the label will show "colorfast" on the back if it is.