Talk:Armor/@comment-3040092-20101001025948

There is a cap that approaches 99% so you can never reach 100%. The formula is %Reduction=Armor/(Armor+100).

If you are playing Rammus and stack 6 Thornmails with Defensive Ball Curl it will look like this.

600 Armor (From Thornmail) 150 Armor (Defensive Ball Curl) 89 Armor (Level 18 Rammus) 839/939= 89% damage reduction

You could get it a little higher with runes and if you include the 21 point defense mastery might be sitting at around 95% physical damage reduction so that's probably about as max as you are going to get.

There are a few other things you could include and squeeze another % or 2 out but chances are the game will be over before it ever gets that extreme. I don't recommend getting 6 Thornmails though.