Standard steel used by most watch companies has a hardness of between 200 and 240 HV (Hardness Vickers is a common scale used to measure material hardness).  The Tegiment layer has a hardness of 1,200 Vickers which is five times harder than standard steel. 

The Tegiment layer is not a coating consisting of a foreign material, instead the steel itself that has been hardened using a special engineering process that creates a hardened barrier. The base material is a type of stainless steel also used for surgical implants, and the stainless steel resistance to corrosion is even further improved by the Tegiment hardening process. 

Tegimented cases are used on the 756, 757, 856, 857, 900, U1000 and U2 Black series.  Tegimented bezels are used on the U1, U2 and UX series.