The environmental scanning electron microscope (ESEM) is a direct descendant of the conventional SEM, but also permits wet and insulating samples to be imaged without prior specimen preparation. A low pressure (up to around 10 torr) of a gas can be accommodated around the sample. When this gas is water, hydrated samples can be maintained in their native state. Whether the gas is water or some other gas, ions formed on collisions between electrons emitted from the sample and the gaseous molecules drift back towards the sample surface helping to reduce charge build up. This eliminates the need for insulators to be subjected to a conductive surface coating. These two key advantages of ESEM open up a wide range of materials to the power of scanning electron microscopy.