There was another reason he selected leather: Xiao Lin's combat style was going to be dual cultivation. Even though Lu Renjia was shocked when he mentioned it, he still gave his best recommendation, which was that leather would be the best option.
Of course, it was just the current situation. Lu Renjia had given Xiao Lin quite a lot of information over the few days. Making gear was a very complicated process, and the material chosen would basically determine what the end product would do.
For instance, heavy armor than had metals as a base would not interact well with spells. Even if they could, it would be high-leveled metals, which were not within Xiao Lin's budget.
For that reason, leather was currently his best choice. It would at least have higher defensive capabilities than a mage's robe.
