Boy flex is a lack of rigidity in a motor vehicle's chassis. It is often something to be avoided by car manufacturers as higher levels of body flex is a sign of structural weakness, and means that the vehicle's suspension cannot work as efficiently - the body takes up some of the 'slack', rather than the parts of the car which were specifically designed for this purpose. A chassis that flexes may be prone to fatigue and further "softening" with use will eventually result in failure. Cars of a sporting nature are, therefore, often very 'stiff', while convertibles or cabriolets are not often considered to be good candidates for high-performance sports cars because of their lack of a rigid roof.