Traditionally, the trapper hat was part of a hunter's gear. Worn in frigid places where ears, chin, and nape needed sure-guard protection from the elements in undiscovered country. The trapper hat we know today, with its telltale earflaps, was worn across North America in colder climates, from the Appalachian Mountains to deep into Canada.
At the outset of World War I trapper hats, referred to as "aviator" hats, were necessary to protect a pilot's head and ears from the frosty winds they faced in the first open-cockpit biplanes to roam over Europe.