When selecting metal interior doors, the choice of substrate is critical. Galvanized steel is the industry standard for rust resistance, while aluminum alloy offers a lightweight, corrosion-proof alternative ideal for modern minimalist designs. For the finish, powder coating is highly recommended as it provides a durable, scratch-resistant surface that does not emit harmful VOCs. If the project requires a high-end aesthetic, look for fluorocarbon (PVDF) coatings or wood-grain heat transfer printing which mimics the look of natural timber while maintaining the structural integrity of metal.