This version of the weaver’s knot is used when smooth yarns won’t hold with a regular weaver’s knot. Remember though, even this knot won’t hold very slippery yarns.
The double weaver’s knot is a regular weaver’s knot with an additional step. One way to make it is to begin like #1, the “ears” method. As soon as you have the thread between the ears, take it once around the right-hand ear as well. Then do the same last steps: take the right-hand ear down under the thumb and tighten by pulling on the right standing end.
The double can also be undone like the regular weaver’s knots.
Taken from Book #2: Warping Your Loom & Tying On New Warps