Fashion has dictated a variety of head adornments. Consider the powdered and pompous wigs of the 18th century or the felted beaver hats of the 19th century — which almost wiped out beaver populations in the New World.

Elaborate Easter bonnets were once all the rage. No self-respecting member of London's high society would appear on the street without a fancy hat during the Regency and Victorian periods. Jackie Kennedy started a fashion craze with her pillbox hats in the 1960s.

Another function of hats is use in rituals, ceremonies and religion. Many religions around the world require their spiritual leaders to wear distinctive clothes and hats, notes Brown. In some cultures, special headgear is thought to not only identify the priest or shaman, but to also help him communicate with the spirit realm.

Head coverings such as the Jewish yarmulke are worn to show respect. At various points in their history, Judaism, Christianity and Islam have all required women to wear head coverings, especially when entering the sacred space of a church, mosque or synagogue.

So, hats serve many purposes, says Brown, and what you'll notice as you look at the exhibit, she says, is that many of the roles overlap.

For example, one of her favorite hats in the exhibit is an elaborate, silver candelabra worn by Egyptian brides a century or so ago. "The tradition was that the bride was escorted to her new husband's home on the night of her wedding. They would carry a candelabra to light the way. Then someone decided that instead of carrying it, she would wear it on her head."

The candelabra hat became part of a ritual. But a more elaborate and fancy candelabra would also indicate the bride's wealth and status.

In addition to how hats are used, the exhibit also shows the wide variety of materials and the creativity and imagination that has gone into making hats. There's a hat made of frog skin — which includes the frog's head on the bill. There's a hat from Romania that is made of a pounded-flat mushroom. A Spanish comb-hat is made of tortoise shell.

Feathers adorn elaborate headdresses from indigenous tribes. Grass and other vegetable fibers make up a Polynesian hat. Porcupine quills are used to create a head-guard. A carved, wooden headband features a slit that hair would be pulled through to add to the decorative quality.

"The variety of forms, sizes, materials and embellishments uncap the secret and privileged world of the hat-wearer," says Brown.