Single drawn hair is hair that have been cut from one donor. Specifically, the hair will be cut from a donor's ponytail. This creates somewhat of a consistency among the strands of hair which will appeal to certain women since the consistency can have a direct effect on the look of the extensions once they are fixed in place. You could say consistency gives a more realistic appearance.
Single drawn hair will have some short strands of hair in them. One thing to note about the short hairs present in the ponytail is that they have to be removed in order to maintain a consistent look. In order to help facilitate this, the hair is commonly sold in the range of 15' to 18' in length. However, it is also possible to find single drawn hair that is in the range of 10', 12',14' in length. Unfortunately, you may find that this type of hair extension is uneven.