What does the term "foil" refer to in hair coloring?

The term "foil" in hair coloring specifically refers to a technique that utilizes strips of aluminum to separate sections of hair during the coloring process. This method is essential for achieving highlights or developing dimensional color in the hair. By wrapping the hair strands in foil, the color can be applied more effectively, preventing it from bleeding onto other sections of hair and allowing for more precise application. The aluminum helps to retain heat, which can enhance the color's development, leading to a more vibrant result.

Other choices describe different aspects of hair care but do not align with the definition of "foil" in the context of hair coloring. For instance, hair dye is a product used for coloring but does not refer to the technique of applying that color, and tools for cutting or methods for curling hair focus on different styling techniques unrelated to the coloring process.