A hardtop is a rigid form of automobile roof, typically metal, and integral to the design, strength, and style of the vehicle. In limited cases a hardtop roof can be detachable (often designed to store in the trunk), or retractable within the vehicle itself. The pillarless hardtop (often referred to as simply "hardtop") is a body style of cars without a B-pillar. Pillarless hardtops The pillarless hardtop (abbreviated as "hardtop") is a post-World War II car body designed with no center or B-pillar or glass frames. If window glass frames are present, they are designed to retract with the window when lowered. This creates an impression of uninterrupted glass along the side of the car. Even the smaller automakers like Packard introduced two door hardtops in 1952 "as a response to America's newly discovered fondness for sportier looking cars that resembled a convertible, but had the comfort and convenience of a two-door sedan." In one instance stylists added faux ribbing to a hardtop roof to make it appear to be like a convertible top, By the mid-1960s optional vinyl roofs became widely available in virtually all model lines, reinforcing the convertible look in hardtops. A pillarless hardtop is inherently less rigid than a pillared body, requiring extra underbody strength to prevent shake. Production hardtops commonly share the frame or reinforced body structure of the contemporary convertible model, which is reinforced to compensate for the lack of a fixed roof. The hardtop design received criticism that its roof structure may not provide adequate protection in the event of a rollover crash. However, subsequent research reported that rates of serious or fatal injury in hardtop models (both 2 and 4-door versions), as well as four-door station wagons, were significantly lower than sedans while the rates of any degree of injury for those same body styles were also significantly lower. A 1980 study for evaluation of rollover test devices reported a greater degree of roof crush was associated with hardtop body styles, but the occurrence of severe passenger injury was not more frequent than in the other car body styles. The hardtop body style 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