The primary function of a fire helmet's __________ is intended to provide thermal protection.

The primary function of a fire helmet's inner liner is indeed to provide thermal protection. The inner liner is designed to absorb and dissipate heat, protecting the firefighter's head from extreme temperatures encountered during firefighting operations. It is typically made from high-temperature resistant materials that can withstand the intense heat generated by flames and hot gases.

This layer works in conjunction with other parts of the helmet, but its specific role is crucial for thermal protection. The outer shell primarily offers structural integrity and impact resistance, while the suspension system is designed to keep the helmet securely in place and ensure comfort. The vapor barrier serves to prevent moisture from penetrating the helmet, but it is not primarily aimed at thermal protection. Therefore, the inner liner is the key component responsible for safeguarding a firefighter’s head against severe heat and thermal hazards.