Most of the materials Saleen used to craft armor for the demons were obtained from magic beast shells from the sea. These shells might be precious, but they had their fair share of flaws too. They were too lightweight. To a human, a lighter armor could raise their efficacy during battle, however, a demon's strength was too shocking. A demon was actually better off having heavier armor.
The heavier the armor, the better. It could absorb impact from a weapon, thus having better defense against heavy weapons.
At the moment, Saleen had gained immense knowledge about crafting armor, he had also obtained a large amount of gorilla metal. He decided to produce new armor for the four demons. As for the style of the armor, Saleen would imitate the Grukos family's Spirit Snake Armor.