Armor is nothing new in Legend of Zelda, in fact, Link's famous outfit is literally chain mail and cloth. He also has gotten numerous upgrades to his defense throughout the franchise history. In Twilight Princess, he gets the opportunity to become truly invincible...for the right price.
After doing two sidequests (and collecting 3,000 rupees), Link get the Magic Armor. A literal invincible armor that Link can wear and take no damage. However, for every second spent in the armor, and blow landed on him, he loses a Rupee. If Link has no Rupees left to lose, the armor will lose it's power. Think that's a waste? Not so fast, if you help Agatha in her quest to become Bug Queen, she'll give you unlimited rupees. Which means you can literally become invincible throughout the game.