Resistors are special equipment only available in the black market. They can be purchased with blood amber or coins. Every rotation offers level I and II resistors of all types but only one type level III resistor. They are commonly used by high level players and are only particularly effective for high level players.
Resistors provide the equipped shield with damage resistance against a particular weapon type. They only mitigate incoming damage for the ship's armor. Shields do not receive any damage mitigation. Resistors can mitigate damage sustained from shield bypass as well. Resistors mass occupy a fraction of a ship's current equipped weight, they are only mass efficient equipped on ships with 6,000+ armor - therefore, not effective for destroyers or battleships when your trying to save weight. Furthermore, since only high level players equip substantial armor on their ships, mid level players and below are advised against purchasing resistors as they are only effective for high level players ships.
Resistors also reducing the damage sustained on armor from shield bypass. They only reduce its specific damage type. For example, Storm drivers with reinforced rails will inflict 30% less shield bypass damage against a ship equipped with a projectile resistor III - but the projectile resistor III would not resist any damage from Arc missiles which have their own built in shield bypass. Remember all weapons bypass shields by 10% because shields only absorb 90% of the incoming damage.
Hybrid Resistors are resistors found in Alien Mobilization and are reuseable items. They combine resists to form another type of resistor which can resist 2 weapon type damages. Currently only Xeno Division Hulls seem able to equip these resistors. They are the most powerful resistors in the game and follow the rules similar to normal resistors.
Black Market Resistors
Xeno Division Resistors