A pith helmet is a type of headgear traditionally worn in tropical climates. It is made from pith, a lightweight material derived from the inner layer of the stem of certain plants. The term 'pith helmet' can refer to two different styles of headgear: the traditional, round-topped helmet, and the more modern, peaked helmet. The four-letter solution TOPI refers to the traditional style of pith helmet, while the five-letter solution TOPEE refers to the more modern, peaked style. The three-letter solution HAT is a general term for any type of headgear.