Since this is a thread on the ARMATA, some more photos and an estimate from TANKNET -- it appears that the Russians might be using advanced heavy ERA to make up for a thinner armor profile than usual.
"Armata is supposed to be using a new type of steel which should provide the same protection to basic RHA steel at 15% reduced thickness. "
This new steel (44S-sv-Sh) is apparently a weldable/machinable version of earlier High Hardness Steels (HHS); which offers slightly better protection per weight/area unit, without having to have the same amount of supporting structure as earlier armor steels (accounting for the reductions).
