To warp means to wind threads around sets of stakes, that may be horizontal or vertical. Most Andean textiles are warp-faced, which means only the warp threads (the lengthwise threads over and under which other threads, called the weft, are passed) are seen in the completed textile. This is due to how closely packed the threads are, thus hiding the wefts (the cross threads in a weaving). Weavers make many of their decisions about textile design during this stage. Warping on a backstrap differs from warping on a horizontal loom.
A backstrap loom has traditionally been used in Andean weaving. This semi-vertical loom, used to create warp-faced cloth, is used by the majority of weavers in Cusco. In horizontal loom weaving, the loom is attached to four upright stakes (tarcapus). The weaver sits in front to weave. With backstrap loom weaving, the warp threads are fashioned securely at one end to a rod, which the weaver fastens in front of her with a band around the waist. The rod is attached at the other end to stakes placed in the ground. In horizontal loom warping, two weavers work together, seated on opposite sides of the loom. They toss a ball of yarn to each other, switching colors according to the previously agreed-upon stripe sequence.