Is the consideration in Wudu' the wiping of the head or the hair?

Wiping the head is the third agreed-upon obligatory act of ablution. It involves wiping the hair or skin on the skull. The method is to place one index finger on the tip of the other, and then place them on the front of the head, with both thumbs on the temples. Then, pass them to the nape of the neck and bring them back to the front of the head. Any other method of wiping is also sufficient.