The hood (North America) or bonnet (Commonwealth) is the hinged cover over the engine of motor vehicles that allows access to the engine compartment for maintenance and repair. In British terminology, hood refers to a fabric cover over the passenger compartment of the car (known as the 'top' in the US). In many motor vehicles built in the 1930s and 1940s, the resemblance to an actual hood or bonnet is clear when open and viewed head-on; in modern vehicles it continues to serve the same purpose but no longer resembles a head covering.
On passenger cars, a hood may be held down by a concealed latch. On race cars or cars with aftermarket hoods (that do not use the factory latch system) the hood may be held down by hood pins. A hood may sometimes contain a hood ornament, hood scoop, power bulge, and/or wiper jets. Hoods are typically made out of steel, but aluminium is rapidly gaining popularity with auto companies. Aftermarket manufacturers may construct hoods out of fiberglass, carbon fiber, or dry carbon.
In Japan and Europe, regulations have come into effect in recent years that place a limit on the severity of pedestrian head injury when struck by a motor vehicle. This is leading to more advanced hood designs, as evidenced by multicone hood inner panel designs as found on the Mazda RX-8 and other vehicles. Other changes are being made to use the bonnet / hood as an active structure and push its surface several cm away from the hard motor components during a pedestrian crash. This may be achieved by mechanical (spring force) or pyrotechnic devices.
A recent trend in street racing has been to raise the rear end of the hood to promote cooling, although this, in theory, does little, except at dead stop, since the area of the hood directly in front of the windshield and the lowest portions of the windshield are almost always positive pressure zones (air actually flows into the engine bay, not out of it, increasing engine bay pressure).