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This article refers to the phenomenon in physics. For other meanings, please see Slipstream (disambiguation).

The slipstream of a moving object is a region of reduced pressure or even suction (negative pressure), exerted in the neighbourhood of the object and in the direction of its movement, and caused by its movement through a medium.

It has been suggested that this article or section be merged with Drafting (racing). (Discuss)

The term "slipstreaming" is most often used in relation to objects moving through air, though not necessarily flying. If a following object, moving at the same speed, can position itself within the slipstream, it will require less energy to maintain its speed than if it was moving independently, because the front object blocks a significant amount of air resistance. Using this principle is called slipstreaming.

Slipstreaming is important in a number of contexts, including:

• Cycling: in fast bicycle races, competitors attempt to 'draft' or use one another's slipstream, breaking to overtake the leader only at the last possible moment. In recreational cycling, on the other hand, members of a group can take turns at the leading position, enabling one another to rest a little. In a group of cooperative cyclists with sufficient group-riding skill, stronger members can spend more time leading, to give weaker riders more rest, enabling riders of different strengths to ride together, at least on relatively flat routes. On hilly routes, the benefit of drafting is relatively less on climbs, when airspeeds are slower and the cyclist's primary effort is working against gravity. The flat or hilly nature of a route has consequences for both racing and recreational cycling, with the different types of routes favoring different types of cyclists. See: drafting. See also: peloton.
• Bird flight, especially during migration: the extended formations or "skeins" in which many migratory birds (especially geese) fly enable the birds (except, of course, the bird at the front) to take advantage of one another's slipstream. Other birds (for example cormorants) that typically fly in close formation even on short journeys are probably also exploiting the slipstream effect.
• Automobile transport: Following another motor vehicle and using care to stay in its slipstream allows for significantly improved fuel efficiency, mostly due to reduced atmospheric drag. Such practice is frequently referred to as drafting. This can be commonly seen in the instance of truck convoys traveling in a single-file queue several vehicles long on highways. One other example is auto racing drivers following each other closely in order to conserve fuel, the better to gain competitive advantage by reducing the frequency of fuel stops made during the course of the race. The principle is also frequently exploited in auto racing to overtake another driver on straights.

• Spiral slipstream - slipstream caused by a rotating propeller.