The IS 250C builds on the L-finesse design characteristics of the IS saloon, with elegant proportions, sweeping lines and contrasting convex and concave surfacing. In spite of its close relationship to the saloon, it only shares a handful of common body elements: bonnet, headlamps, door handles and door mirrors. All other body panels have been redesigned to harmonise with the convertible's folding roof.
The front overhang has been increased by 15 mm to improve aerodynamic efficiency when driving with the top down. There is also a new fog lamp design, integrated in the deep front air dam. In profile the IS 250C is characterised by muscular coachwork below a pronounced, rising beltline that kicks up towards the rear. The steeply raked windscreen flows seamlessly in the aerodynamic arc of the roofline, while the crisp C-pillar is integrated into the folding roof structure.
In coupe guise, the cabin tapers towards the rear, giving a fluid transition from the roofline through the C-pillar to the luggage compartment. At the rear there are new combination light clusters with distinctive linear LED illumination, and a high-mounted LED stop light built into the upper lip of the boot lid.
The IS 250C shares the saloon's high levels of interior luxury and practical innovation, with a number of bespoke technical revisions to ensure the on-board comfort and entertainment systems work effectively when driving in convertible mode. The low profile front sports seats are heated and ventilated and have a new arched frame with an integral seatbelt guide. Extra comfort for top-down driving is provided by additional heating pads at shoulder height, increased heater capacity and greater ventilation airflow.
The two full-size rear seats are set 30 mm further inboard than those of the IS saloon to optimise headroom and are separated by a centre console with integrated cupholders. Access to the rear seats is made easier by an increase of 300 mm in the length of the front doors, compared to the saloon. The front seats have a one-touch walk-in button which automatically folds and slides the seat forwards.
Generous luggage space has been achieved by lengthening the rear overhang by 50 mm and exceptionally compact packaging of the folding roof structure. With the hard top in place capacity is 583 litres; with the roof down it is 235 litres.
The instrument panel and surrounding interior components are the same as on the IS saloon. However, the instrument binnacle has been extensively revised to ensure visibility in open-top driving. The dial colour has been changed, LED contrast increased and the transmissivity of the glass reduced from 30 to 20 per cent. The shape of the needles has been changed and the dials themselves gain metal-tone bezels, and the central multi-display screen adds a hard-top operation status indicator. The scrupulous attention to detail extends to the rear view mirror, which has a shorter, strengthened mount to minimise shake.
The climate control system has been configured for top-down motoring with the addition of a speed sensitive control that automatically increases air flow in roof-down mode, further increasing the flow according to vehicle speed.
The LCD touch screen controls for the audio and navigation systems have been improved with a redesigned set-up screen and extra tabs for the audio functions. Both the standard eight-speaker 246W premium sound system and the 12-speaker 365W Mark Levinson Surround System gain equaliser tuning to provide consistent audio quality whether the roof is up or down, automatically adapting to the loss of bass when the roof is stowed.