It’s generally recommended to wash your fabric and to then leave it damp before tie-dying because the dye has an easier time saturating the fabric when it’s wet.
However, this also depends on the look you want and technique you use. You can apply the dye to dry fabric, just make sure it has been washed if it is new. Using dry fabric will result in a higher color saturation but a less uniform permeation throughout your fabric.
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