Steel Fiber

Steel Fiber is a common warframe mod that increases the frames Armor.

It can be dropped by any of the three factions and has a polarity type.

Due to the way armor is calculated (chart can be found below), it is not recommended to use this mod on low base armor warframes.

Calculations
Armor is calculated as Armor /(Armor+100), which is then multiplied with the damage received. For example, 50 damage passing through 100 armor calculates as 100/200 * 50, resulting in 25 damage reduced by armor. Note that armor does not apply to shields which take 200% damage from ice attacks and 100% from everything else.

Steel Fiber increases the base armor by the specified percentage, which is then applied to the above calculation. For example 100 armor with a 50% Steel Fiber comes to 150 armor, when applied to 50 damage calculates as 150/250 * 50 = 30 damage reduced.