Which feature is essential for adjusting the fit of a helmet?

An adjustable chin strap is essential for adjusting the fit of a helmet because it helps secure the helmet in place, ensuring that it fits snugly on the head. A proper fit is crucial for the helmet to provide effective protection, as a loose helmet may shift during impact or movement, reducing its effectiveness in preventing injuries. The chin strap allows users to customize the fit to their individual head shape and size, making it a critical feature for safety.

While ventilation holes contribute to comfort by allowing airflow and reducing heat buildup, they do not play a role in adjusting the fit. Decorative stickers do not influence helmet performance or fit; they are purely aesthetic. Foam padding, although important for comfort and impact absorption, primarily serves to cushion the head and absorb shock rather than adjust the overall fit. Thus, the adjustable chin strap stands out as the key feature necessary for ensuring the helmet is securely positioned on the user's head.