A hardtop is a term for a rigid, rather than canvas, automobile roof. It has been used in several contexts: detachable hardtops, retractable hardtop roofs, and the so-called pillarless hardtop body style.
Following the ascendancy of steel tops for closed bodies in the 1930s, detachable hardtops with metal roofs began to appear. After World War II, the availability of new types of plastic and fiberglass allowed lighter, easier to handle hardtops with much of the strength of a metal top.
In the 1950s and 1960s detachable hardtops were offered for various convertible sports cars and roadsters, including the 1955-1957 Ford Thunderbird and the Chevrolet Corvette. Because the convertible top mechanism is itself expensive, the hardtop is customarily offered as an additional, extra-cost option. On early Thunderbirds (and Corvettes through 1967), buyers could choose between a detachable hardtop and a folding canvas top at no additional cost, but paid extra for both.
Improvements in canvas tops have rendered the detachable hardtop less common in recent years, in part because the top cannot be stored in the vehicle when not in use, requiring a garage or other storage facility. Nonetheless, some open cars continue to offer it as an option. Around 10% of Mazda MX-5s are believed to have been delivered with an accessory hardtop, which is compulsory for some auto racing series.
A Retractable Hardtop (also known as coupé convertible or coupé cabriolet) is a type of convertible that forgoes a folding textile roof in favor of an automatically operated, multi-part, self-storing roof where the rigid roof sections are opaque, translucent or independently operable.
The other automotive usage of the term "hardtop" is a body style known as the hardtop convertible. A hardtop convertible is a fixed-roof model designed to look like a convertible with the top raised. While some early models retained side window frames and B-pillars, by the 1950s most were pillarless hardtops, omitting the B-pillar (the roof support behind the front doors) and configuring the window frames, if any, to retract with the glass when lowered. Some hardtops took the convertible look even further, including such details as simulating a convertible-top framework in the interior headliner and shaping the roof to resemble a raised canvas top. By the late 1960s such modifications were often superseded by a simple vinyl roof.
A pillarless hardtop is inherently less rigid than a pillared body, requiring extra underbody strength to prevent shake. Production hardtops commonly shared the frame or reinforced body structure of the contemporary convertible model, which was already reinforced to compensate for the lack of a fixed roof. With such a reinforced frame, a hardtop was stronger and stiffer than a convertible, but both weaker and (because of the reinforcements) heavier than a pillared body.
There were a variety of hardtop-like body styles dating back to at least the 1920s. Chrysler Corporation showed a pillarless Town and Country hardtop coupe as a concept vehicle in 1946, but the car never went into production. The trend-setter for mass-production hardtops was General Motors, which launched two-door, pillarless hardtops in 1949 as the Buick Roadmaster Riviera, Oldsmobile 98 Holiday, and Cadillac Coupe de Ville. They were purportedly inspired by the wife of a Buick executive who always drove convertibles, but never lowered the top. The hardtop became extremely popular in the 1950s, and by 1956 every major U.S. automaker offered hardtop coupés and four-door sedans in a particular model lineup. In 1955, Buick and Oldsmobile introduced the first 4 door hardtop sedans and Chevy and Pontiac even introduced "hardtop" (six pillar) two door wagons (the Nomad and Safari, respectively), and in 1956 the first four-door hardtop station wagon was introduced by Rambler. In 1957, Mercury offered both two- and four-door hardtop wagons, the only brand to ever to do so. The type didn't didn't catch on, though, as most buyers considered wagons too boxy to benefit from the sporty look (or expensive enough to begin with). All disappeared from the market after 1964.
Throughout the 1960s the two-door pillarless hardtop was by far the most popular body style in most lines where such a model was offered. Even on family vehicles like the Chevrolet Impala, the two-door hardtop regularly outsold four-door sedans.
The hardtop began to disappear along with convertibles in the mid-1970s, partly out of a concern that U.S. federal safety regulations would be difficult for pillarless models to pass. The ascendancy of monocoque construction also made the pillarless design less practical. Some models adopted modified roof styling, placing the B pillars behind tinted side window glass and painting or molding the outer side of each pillar in black to make them less visible, creating a hardtop look without actually omitting the pillar. Some mid to late 1970s models continued their previous two-door hardtop bodies, but with fixed rear windows or a variety of vinyl roof and opera window treatments. The U.S. industry's last true two-door and four-door hardtops were in the 1978 Chrysler Newport and New Yorker lines.
Since then, no U.S. manufacturer has offered a true hardtop in regular production, although some German manufacturers, including BMW and Mercedes-Benz have offered upscale pillarless hardtops. Many Japanese domestic cars, particularly from Toyota and Nissan, are offered in hardtop form. British luxury carmaker Bentley (owned by Volkswagen Group) sells two true hardtop coupes, the Continental GT fastback, and the new Brooklands coupe (2008). The body style was thought to be making a comeback, as concept versions of the Dodge Challenger and Chevrolet Camaro shown in 2006 were both two-door hardtops, though both companies have stated that production versions will contain a B Pillar to keep the prices low. Another pillar-less design was featured in the 2007 model concept for the Chrysler 300C.