Sapma designs look very similar to supplementary weft patterns from non-Bhutanese weaving traditions, except that the Bhutanese technique is not visible on the reverse of the fabric. The other difference is that thread ends are worked as pairs.
Pattern threads are laid in with the weft with both ends protruding on the front of the cloth. On second and subsequent rows, the two ends are crossed behind the pattern warps that are raised with a pick up stick:
Sapma is worked on every row, and so suits motifs with diagonal sides.
Sapma motifs are often combined with Thrima lines to produce complex designs, or “flowers” as I hear Bhutanese call them.