This mod changes armor so that instead of reducing damage taken it increases the player's max health. It does this by replacing the armor's default attribute modifiers which give armor points with an attribute modifier that increases max health by a value based on how many armor points you would get from that armor piece. That value is obtained by multiplying the amount of armor a piece gives by a value set in the config.
There is nothing else to explain about this mod, so here is a quick demonstration:
Before equipping a piece of armor, its attribute modifiers are the same as in vanilla.
After equipping a piece of armor, its attribute modifiers change to one that increases your max health by a value based on the amount of armor the piece originally gave and the armor no longer gives any armor points.