Comment by Choco on Nageki no Bourei wa Intai Shitai - Saijiyaku Hanta ni Yoru Saikiyou Patei Ikusei Jutsu - Chapter 25

@Choco could it be that it nullifies magic co  contact, or it's a horrible material to wear around like lead or galena

@Choco you have to remember that it'll also negate positive magic like healing

@Aqua ah indeed.

which means the guy in armor probably would be best as a rouge that ambushes mage groups then rather than fight head on