What type of gels cannot be removed with a solvent and must be filed off the natural nail?

Certain gels, particularly hard gels, are formulated to provide a strong, durable finish that adheres tightly to the natural nail. These types of gels create a bond that is resistant to solvents like acetone or other nail polish removers, making them unsuitable for removal through soaking. Instead, they require mechanical removal, which involves filing them down until they are fully taken off the nail surface.

This process is essential in maintaining the integrity of the natural nail, as using solvents might not effectively dissolve the hard gel and could potentially lead to damage. In contrast, other types of gels, such as soak-off gels, can be easily removed with solvents designed specifically for that purpose. Therefore, the correct choice highlights the nature and removal process of hard gels distinctly.