Porcupine fishes inflate their bodies dramatically as a form of defence. If killed in this state, the skin retains its distended shape and can be dried before being gutted and lined for wear. Helmets made in this way were worn by warriors in the Gilbert Islands (now Kiribati) with body armour made from coconut fibre. They were probably too fragile to protect the wearer against a direct blow to the head and so may have been designed primarily to show status and intimidate the enemy. 

Presented to Prince Philip, Duke of Edinburgh at Tarawa by the Island Communities of Beru Island during his visit to the Gilbert and Ellice Islands, 25 March 1959.