The Diablo 2 Wiki
The Diablo 2 Wiki archive is available for anyone looking for information on Diablo 2. All information here is pre-D2R but contains a lot of useful information that is still relevant. Updated sections for new D2R features can be found on the PureDiablo Diablo 2 section

Iron Skin

From Diablo 2 Wiki

Iron Skin

Iron-skin.jpg

Required Level: 18

Prerequisites: None
Notes: Iron Skin greatly increases the Barbarian's defense, and is a prerequisite for the extremely-useful Natural Resistance. Most barbarians are fine with just a few points in this skill, but builds that require high defense will want to max it, and pair it with high level Shout for the utmost defensive capacity.

Skill Level Progression [e]
Slvl Defense +X%

Slvl Defense +X%

Slvl Defense +X%

Slvl Defense +X%

1 30% 6 80% 11 130% 16 180%
2 40% 7 90% 12 140% 17 190%
3 50% 8 100% 13 150% 18 200%
4 60% 9 110% 14 160% 19 210%
5 70% 10 120% 15 170% 20 220%