Which product is least likely to provide hold for hairstyles?

Leave-in conditioner is designed primarily to moisturize and detangle hair, making it easier to manage without necessarily providing any structure or hold for hairstyles. Its formulation focuses on hydration and nourishment rather than styling, which means it won't contribute to the firmness or longevity typically desired in styled hair.

In contrast, hair gel, hair spray, and mousse are all specifically crafted for styling purposes. Hair gel provides a strong hold, making it suitable for defined styles, while hair spray is often used to set styles in place and provide lasting support. Mousse can add volume and some level of hold, allowing for a soft structure that enhances the natural form of the hair. Therefore, a leave-in conditioner stands out among these products as it does not contribute to the styling aspect, focusing instead on the health and maintenance of the hair.