A funnel is a pipe with a wide, often conical mouth and a narrow stem. It is used to channel liquid or fine-grained substances into containers with a small opening. Without a funnel, much spillage would occur.
Funnels are usually made of stainless steel, glass, or plastic. The material used in its construction should be sturdy enough to withstand the weight of the substance being transferred, and it should not react with the substance. For this reason, stainless steel or glass are useful in transferring diesel, while plastic funnels are useful in the kitchen. Sometimes disposable paper funnels are used in cases where it would be difficult to adequately clean the funnel afterwards (for example, in adding motor oil to a car). Dropper funnels, also called dropping funnels or tap funnels, have a tap to allow the controlled release of a liquid.
The term "funnel" is sometimes used to refer to the chimney or smokestack on a steam locomotive or a ship. There is also a type of spider known as a funnel-web due to its habit of building its web in the shape of a funnel. The term "funnel" is even applied to other seemingly strange objects like a smoking pipe or even a humble kitchen bin.
When used with filter paper, filter funnels, Buchner and Hirsch funnels can be used to remove fine particles from a liquid in a process called filtration. For more demanding applications, the filter paper in the latter two may be replaced with a sintered glass frit.
Glass is the material of choice for laboratory applications due to its inertness compared with metals or plastics. However, plastic funnels made of nonreactive polyethylene are used for transferring aqueous solutions. Plastic is most often used for powder funnels which do not come into contact with solvent in normal use.
In popular culture, the Tin Woodman in L. Frank Baum's classic novel The Wonderful Wizard of Oz (and in most dramatizations of it) uses an inverted funnel for a hat, though that is never specifically mentioned in the story - it originated in W.W. Denslow's original illustrations for the book.