Prior to Damage 2.0, this mod increased resistance to Laser damage. Though Laser damage was removed from the game when Damage 2.0 rolled out, the mod card still claimed to increase laser resistance for quite some time.
This was later changed to Radiation damage.
Like all resistance mods, this worked by subtracting its resistance value from Radiation's damage type modifier against both the shield type and the health type of the Warframe who equipped it, but not armor. As a result, this increased the user's effective shields against Radiation by +150% and effective health against Radiation by ~+81.8%.
Update 18.13.3 once again changed the function of this mod. The element resistance was changed from Radiation to Blast, however this was not mentioned. It was later changed to Radiation again also without being mentioned, meaning the change to Blast was most likely unintentional.
Before Update 9.5, it was uncommonly dropped in the Void and rarely dropped on other maps. As of Update 9.5, this mod can be found in normal maps.