Which product is commonly used to achieve a sleek finish on straightened hair?

Hair serum is commonly used to achieve a sleek finish on straightened hair due to its ability to smooth the hair cuticle and reduce frizz. Serums typically contain silicone or other emollients that provide a glossy appearance while also helping to protect hair from heat damage caused during the straightening process. When applied to finished styles, serums can impart shine and create a polished look, which is especially desirable for straightened hair.

The other products listed serve different functions. For instance, dry shampoo is used to absorb excess oil and refresh hair between washes, rather than adding shine or smoothness. Texturizing spray is intended to enhance volume and texture, making hair look more tousled rather than sleek. Volumizing mousse is designed to add body and lift to hair, which is the opposite of the sleek finish desired for straightened styles. Thus, while all these products have their uses in hair styling, hair serum is the standout choice for achieving that smooth, sleek finish on straightened hair.