The Kentucky Derby style of grand hat is notably known for its appearance at the Kentucky Derby. However, they are perfect for all year long to protect from the sun. Here is a little history behind the significance of the hats.
Colonel Meriwether Lewis Clark Jr., and his wife, Mary, wanted to bring the luxury style of racing in Europe to the United States. In 1875, Mary started the trend of wearing the extravagant hat and encouraged other ladies to do the same. After that, every year more and more people began wearing the hats and lavish outfits.
It was also mentioned that the hats were considered a sign of good luck, so the bigger the hat the more luck it would bring to the race. Now these hats are symbolic and a tradition to carry on when attending the derby.
Source: https://www.forbes.com/sites/micheleherrmann/2020/09/04/kentucky-derby-hats/