In the embroidery technique of underside couching, also known as Opus Anglicanum (English Work), thread (often gold) is laid on the surface of the ground fabric, then couching threads are passed over it. As each couching stitch is worked over the gold thread, the needle is carefully re-inserted into the hole in the ground fabric that the needle created on the way out. The couching thread is pulled tight and a tiny loop of the gold thread from the surface is pulled through the hole in the ground fabric to the underside (thus giving the technique its name).
This creates a hinge in the gold thread, allowing the fabric to bend and giving it a great flexibility. Fabric worked with gold thread in underside couching has much more drape than fabric with surface couched gold, thus making it a much better technique for working objects which will be worn, such as ecclesiastical vestments.