The best wick cord is nylon. Cotton is good capillary rates, but not as good as nylon. This is according to a study below...
Also cotton eventually rots because bacteria will slowly eat the cotton, so eventually it needs replacement. It is not a long term solution. If you want less work, nylon out performs cotton.
https://www.researchgate.net/publication/269730344_Performance_analysis_on_inclined_solar_still_with_different_new_wick_materials_and_wire_mesh
