The kneaded eraser, is also known as putty rubber as it resembles putty or gum. It functions by adsorbing and "picking up" graphite, charcoal and pastel particles. There is no wearing away to leave behind residue, therefore it lasts much longer than other erasers.
Kneaded erasers are commonly used for correcting and lightening charcoal and pastel work, for cleaning slides and final drawings. It is a soft pliable eraser that is extremely kneadable and absorbent.
Small amounts can be "pinched" off the rectangular block in order to work on minute detail. The small pieces can be worked and kneaded by hand to any shape (hence the name) for precision erasing and detailing work. It can become saturated to the point it is no longer able to absorb which will then leave marks instead of erasing. If the eraser is too warm, it may smear or stick.