By which name is the Asian conical hat known in Vietnam?

The Asian conical hat, commonly known as an Asian rice hat, coolie hat (in the UK), oriental hat or farmer's hat, is a simple style of conical hat originating in East, South and Southeast Asia; and notable in modern-day nations and regions of Bangladesh, Bhutan, China, Cambodia, Northeast India, Indonesia, Japan, Korea, Laos, Malaysia, Myanmar, Nepal, Philippines, parts of Outer Manchuria, Taiwan, and Vietnam.

This style of hat is used primarily as protection from the sun and rain. When made of straw or matting, it can be dipped in water and worn as an impromptu evaporative-cooling device. It is also widely understood in East Asia, most notably Japan, as a symbol of Buddhism, as it is traditionally worn by pilgrims and Buddhist monks in search of alms.

In Vietnam, the nón lá ("leaf hat") forms a perfect right circular cone which tapers smoothly from the base to the apex. Special conical hats in Vietnam contain colourful hand-stitch depictions or words while the Huế varieties are famous for their nón bài thơ (lit. poem conical hats). These contain random poetic verses and Hán tự which can be revealed when the hat is directed above one's head in the sunlight. In modern times, they have become part of Vietnam's national costume.