The prospect of another car that's had its fixed roof scrapped and replaced with a folding item is hardly big news. Hey, you can even get a Mitsubishi Colt or Ford Focus with a doffable tin-lid.

Then you look at Lexus' claims about its new IS 250C and perversely, it becomes an extremely interesting car. It's an almost entirely different car to the four-door donor vehicle, given the exterior's only carry-over items are the bonnet, headlights and wing mirrors.

The back end is where most of the action has happened, that is, providing a big enough boot to stow the three-piece roof. Yes, the 250C has a big bustle, but one that just about works stylistically, apart from some unresolved lines from the C-pillar to the rear wheelarch. Roof up, there's a massive amount of luggage space; stowed, there's not much at all, but at least what's available is behind the folded roof, not underneath and virtually inaccessible as with some other convertible hardtops.

Chief engineer Keiichi Yoneda said it was a major job to design the roof and still retain Lexus' NVH parameters. To that end, he utilised 13 electric (rather than noisier hydraulic) motors for the folding process, and no less than 33 sensors to verify its operation, including one that recognises low garage roofs. Good thinking.

There's also a good 60kg of additional body strengthening components, including seven under-floor cross braces. Together with another 60kg of new roof mechanism and 30kg or so of related paraphernalia (such as folding rear headrests for a sleeker look) and extra spec in higher-end models, it all equates to a convertible up to 150kg heavier than the 1625kg IS 250 sedan.

There are three spec levels, all sharing identical 2.5-litre V6, six-speed auto drivetrains. All get touch-screen sat-nav, heated seats and rear parking sensors, with prices starting at $79,900 for the Prestige, $84,900 for the Sport (with its 18-inch rims and radar cruise control) while the Sports Prestige tops the range at $99,900. In comparison, BMW's 325i Convertible auto starts at $100,088.

The best news is that the IS 250C is nice to drive. The ride is velvety smooth without being wallowy, the steering has plenty of feel and road and wind noise levels are low. And yet there are decent levels of grip and handling precision, at least on the 18-inch tyre package.

The drivetrain is just as refined and there are paddleshifts (even in full-auto mode) to help you fully exploit the rev range. As it happens, they're essential: with only 153kW and 252Nm to propel a fair mass, the folding hardtop IS 250 lacks mid-range grunt on uphill country roads. We're told a 3.5-litre V6 version available in the US won't come here in the foreseeable future.

Roof off, cruising through a sunny urban environment, this is an automotive analgesic to the outside world. Red hot performance it might not have, but the IS 250C's refinement, interior comfort and build integrity make it an alluring proposition for summer.

Lexus IS 250C Sports Prestige

2500cc V6, dohc, 24v
153kW @ 6400rpm
252Nm @ 4800rpm
6-speed automatic
9.0sec (claimed)