A cold air intake is a device used to bring lower temperature airflow into a car's internal combustion engine to increase engine power and efficiency. Standard  intake systems tend to be very restrictive, in order to eliminate engine noise. Aftermarket air intake systems come in many different colors and sizes, and are easy to install when compared with other performance-increasing modifications. All  air intakes operate on the principle of increasing the amount of oxygen available for combustion with fuel. Because cooler air has a higher density (greater mass per unit volume),  air intakes generally work by introducing cooler air from outside the hot engine bay. One of the disadvantages are  hydrolock - The intake is lower, and more likely to introduce water into the engine when fording streams or flooded roads. Hydrolock generally does not occur unless the filter is fully submerged in water."Bypass filters" can be purchased which prevent any water of any kind from entering the engine. Air intake systems come in many different styles and can be constructed from plastic, metal, rubber (silicone) or composite materials (fiberglass,carbon fiber or kevlar). The most efficient air intake systems utilize an air box which is sized to complement the engine and will extend the powerband of the engine. The air intake snorkel (opening for the intake air to enter the system) must be large enough to ensure sufficient air is available to the engine under all conditions from idle to full throttle. Under some conditions intake system efficiency can be lost if the intake opening for the airbox is too large. The most basic air intake replaces the stock airbox with a short metal or plastic tube leading to a conical air filter, called a short ram air intake. The power gained by this method can vary depending on how restrictive the factory airbox is. The placement of the filter is usually directly in the engine compartment. The overall benefits depend on the specific application. Power may be lost at certain engine speeds, and gained at others. Because of the increased airflow and reduced covering, intake noise is usually increased. This effect is usually amplified on applications where a resonator, a part intended to reduce intake noise on some vehicles, is replaced by the intake.

A well designed intake use heat shields to isolate the air filter from the rest of the engine compartment, providing cooler air from the front or side of the engine bay. Air bypass valves are gaining popularity in  air intake manufacturing. An air bypass valve is a filtered spacer that is positioned more into the engine bay, between two connected pieces of the cold air intake assembly. This prevents hydro-locking by providing an alternate route for air to come in, thus eliminating the vacuum that causes water to be sucked in from a puddle. Foam filters are a simple piece of foam that is air permeable, and most have no valve. It is argued that this reduces power, but in actuality it provides more surface area for air to enter the engine when the driver accelerates. When driving at moderate speeds, the suction caused by the engine is not enough to activate the air bypass valve. Cloth filter bypass valves only allow air in if the valve is sucked open as result of the vacuum pressure caused by a blocked filter at the bottom of the intake. When it comes to cold air intakes this is the "best of both worlds". Some units are very popular and are known by the brand names such as: AEM, Fujita, AFE, Injen, K & N, weapon R and others are also available.

• provides more oxygen for the engine to burn
• providing a more direct route to the air intake
• more efficient, less restricting  air filter