Final answer:
The firefighter's personal protective equipment item worn on the head for thermal protection is known as a thermal hood, often made from Nomex material.
Step-by-step explanation:
A part of a firefighter's personal protective equipment designed to be worn over the head and under the helmet, providing thermal protection for the neck and ears, is called a thermal hood. This equipment is essential for firefighters as they face intense heat and potentially dangerous environments. A well-known material used for such hoods is Nomex, which can also be found in racing equipment. For instance, wildland firefighters wear Nomex shirts and trousers, and racing car drivers use various Nomex items, including balaclavas and other protective clothing, designed to shield them in case of a fire.