Full Grain leather is defined by Leather Industries of America (LIA) and the American leather manufacturing industry that it represents as:

“The grain split of a hide from which nothing has been removed except the hair and associated epidermis.”

The surface of full grain looks like in this picture under the microscope.

The above definition is consistent with the official definition promulgated by the International Council of Tanners (ICT), the International Union of Leather Technologists and Chemists Societies (IULTCS), and the International Organization for Standardization (ISO) which is as follows:

“Leather bearing the original grain surface as exposed by removal of the epidermis and with none of the surface removed by buffing, snuffing or splitting.”

Top Grain leather is the same as full grain leather.