What are the different types of materials used for upright piano keys?

The different types of materials used for upright piano keys are typically plastic, ivory, and wood. Plastic keys are the most common nowadays due to their durability and cost-effectiveness. Ivory keys were used in older pianos for their smooth texture and aesthetic appeal, but they are now illegal to use due to conservation concerns. Wood keys are also used in some high-end pianos for their unique feel and resonance.