Stearate is a dry lubricant, chemically similar to soap, it makes the surface of the abrasive resistant to clogging which provides a more uniform result and extends the life of the abrasive.
The particles in these abrasives are Aluminium Oxide - the stuff that rubies and sapphires are made from - at around four times as hard a garnet it is very durable indeed. The abrasive particles are applied in an open coat - separated from each other - improving flexibility and giving a more uniform finish.
Particularly effective on very soft or resinous timbers and for keying painted surfaces. This versatile general purpose abrasive works well on all types of timber as well as ferrous and non ferrous metals.