The wool hat commonly worn by Sherlock Holmes is known as a deerstalker. This hat earned its name as common headwear for hunters during the Victorian era.
Sherlock Holmes' deerstalker hat features two flaps joined together at the top of the hat by a ribbon and a rim on both the front and back. The wool fabric is traditionally checkered, but different versions of the Holmes character varied the color and pattern of the fabric. In the original depictions, Sherlock wears his deerstalker hat when in the country, never in town. This is not true in later adaptations of the Holmes character.