With that plan in mind, Kain decided to select the star-attribute as the basis of his armour. It is an attribute that is resistant against most other attributes, and will therefore provide great defense even without any defensive sigils being used. Additionally, it's a flexible attribute that won't reject being engraved by sigils of other attributes if Kain wishes to do so.
Additionally, while Kain had heard briefly about other cultivation techniques used by other nations in lectures and casual conversations with others, the cultivation technique used by those in the Celestial Empire happens to be one that uses star-attribute energy. Therefore, sigils geared towards boosting spiritual power, restoring spiritual power, or increasing the proficiency of his usage of spiritual power would likely be more effective using a material of the star-attribute.
