Which type of gel should be used to create an arch for a client with flat nails?

Builder gel is specifically designed for creating structure and strength in nail enhancements, making it the optimal choice for clients with flat nails. It has a thicker viscosity than other types of gel, allowing it to be molded into an arch that enhances the shape of the nail. This arch is important for both aesthetic appeal and functionality, as it not only improves the overall look but also provides added strength and support to the nail.

Base gel is typically used as a foundation layer for nail enhancements and does not have the thickness needed to create an arch. Top coat gel is applied at the end of the nail service to provide a glossy finish and is not formulated for shaping or structural support. Polymer gel, while versatile, primarily focuses on providing a lighter texture but lacks the specific structural properties necessary for creating an arch in flat nails. Thus, builder gel is the most suitable choice for achieving the desired outcome in this scenario.