Router bits are made of extremely hard and durable materials like carbide. They are designed to cut through relatively tough materials like wood at very high revolutions per minute and must withstand the heat generated from friction.
Most router bits have curved blades, making them challenging to sharpen. These blades on these bits require professional sharpening with the right equipment and should not be entrusted to just anyone. The use of three different grits of diamond sharpening stones is necessary to achieve a sharp edge.