A hat brim is that part of a

hat A hat is a head covering which is worn for various reasons, including protection against weather conditions, ceremonial reasons such as university graduation, religious reasons, safety, or as a fashion accessory. Hats which incorporate mecha ...

that extends outwards and to the side of the head, protruding from the base of the crown.''Glossary of Hat Terms''
at tenthstreethats.com. Retrieved 29 March 2023. Hat brims run around the whole of the crown and come in varying widths. It is also called a bill. The outer edge of the brim may have trim made of leather, silk or ribbon material and is known as the brim binding. The brim protects the eyes from both sun glare and

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...

. The broader the brim, the greater its protection function, but the easier it is for the hat to blow off due to the larger surface area available for the

wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...

to act on. Hat brims are often decorative, for example, on very wide women's hats. If a brim-like element is only attached to part of a hat, it is called a

cap A cap is a flat headgear, usually with a visor. Caps have crowns that fit very close to the head. They made their first appearance as early as 3200 BC. Caps typically have a visor, or no brim at all. They are popular in casual and informal se ...

and this partial brim is known as a

peak Peak or The Peak may refer to: Basic meanings Geology * Mountain peak ** Pyramidal peak, a mountaintop that has been sculpted by erosion to form a point Mathematics * Peak hour or rush hour, in traffic congestion * Peak (geometry), an (''n''-3)-di ...

if at the front, a havelock if it protects the neck, or ear flaps if at the side. In

forensic medicine Forensic medicine is a broad term used to describe a group of medical specialties which deal with the examination and diagnosis of individuals who have been injured by or who have died because of external or unnatural causes such as poisoning, assa ...

there is the so -called "hat brim rule", whereby an injury located above the hat brim line is probably the result of a blow to the head, whereas a fall would result in a wound at the hat brim level. This is used to assign an injury to an accident or a third-party.Kremer et al. (2008)
pp. 716–719.

References

Bibliography

* Kremer, Celia, Stéphanie Racette, Charles-Antoine Dionne and Anny Sauvageau (2008). "Discrimination of Falls and Blows in Blunt Head Trauma: Systematic Study of the Hat Brim Line Rule in Relation to Skull Fractures" in ''Journal of Forensic Sciences'', Vol. 53, Issue 3. Montreal. pp. 716–719. Hats {{clothing-stub