What do the 1982 Ford Sierra, 1985 Mercury Sable and 1988 BMW Z1 have in common? Xenoy.
The difference is the extent and application of its use on the BMW. While Ford and Mercury made use of Xenoy on the bumpers, the Bavarian firm used it on the sliding doors, the wings and the rocker panels. The rocker panels are huge on this car so that’s a lot of plastic.
Xenoy is a development of a polycarbonate known as Lexan, first used at the end of 70s. The polycarbonates are thermoplastic polymers and are useful for their mouldability, and physical strength. Some of them are transparent and we know them as headlamp covers. The first polycarbonates tended to be brittle and GE undertook work to improve their impact resistance.
The next step involved making the material resistant to petrol and then eventually making it amenable to reliable painting processes. The self-coloured blend of Xenoy appeared on the Ford Sierra and that colour was black. Thus the material directly affected the appearance of the car. The advantage of the black plastic bumper lay in knock-resistance and the reduction in weight. Suddenly a lot of the body-in-white could be replaced by a lighter piece of plastic of a more complex shape than could be realised economically and physically in metal.
The later type of Xenoy, CX1101 resolved the problem of self-colouring and also, in a way, confounded the idea of truth-to-materials. Or else it exposes that idea for what it is, empty-designer talk. What, after all, does plastic “look like”? Pretty much anything you like, as it happens and being able to paint plastic to look the same as metal makes for a better looking car.
Now we turn to the BMW. Whereas Ford remained content to make bumpers out of Xenoy, a large area of the 13 exterior panels of the Z1, designed by Harm Lagaay, used Xenoy. A stiffer compound was used for the bonnet and bootlid and folding top cover. Because the materials had different elasticities the clear lacquer used needed to be flexible to match. For the bumpers BMW used foam-filled reinforced fibres and the doors used lightweight thermoplastic.
What we can get out of this is that the distinctive sculptural quality of the BMW derives in large part from the kinds of surfaces made possible (and ruled out) by the qualities of the plastics used. The shutlines are remarkably few in number and show a remarkable discipline. Note that one line connects the front bumper-to-wing line, rocker panel to front wing and rocker panel to rear bumper. The door’s lower edge is aligned to this.
In case you are wondering, the Pontiac Fiero used a different mix (source): “Sheet Molded Compound was used for the hood, roof, rear upper quarter, and rear decklid. Reinforced Reaction Injection Molded urethane was used for fenders, door panels, and lower rear quarters. The rear lowers were later changed to injection molded nylon. RIM Reaction Injected Molded urethane was used for front and rear fascias. Thermoplastic Olefin was used for rocker panels and finally Bexley resin blow-molded by DuPont. This material (not fiberglass) was used for the spoiler or “wing”.” Judging by that long list, GM needed a wide variety of materials for their car’s body whereas BMW got away with a variant of one.
At the time BMW were very excited about the prospects of easily face-lifting the car and for customers to swap the body panels if they felt like it. They also predicted a more widespread application for the body-panel composition.
As it happened none of that came about. The Z1 managed to be a disappointment despite Kacher’s gushing that it was “almost impossible to explore the limits of the Z1” and that “nobody expected this sort of roadholding from a BMW”. It wasn’t facelifted. No-one had different coloured panels for the weekend and today BMWs still have bodies mostly made of sheet steel.
Driven To Write 
Perhaps the clue to the car industry’s failure to adopt plastics for external skin panels is to be found in Bob Lutz’s “Car Guys vs. Bean-counters”, with reference to the Saturn S Series:
“In practice, however, the plastic panels were finicky. They took longer to produce than conventional stamped steel, and they grew and shrank when the temperature changed, requiring the cars to have wide, unappealing gaps around the doors, hood and trunk for clearance.”
Some industries would accept that sort of constraint, but not the shut-line obsessed Germans.
A plastic model kit for the cover photo. Very clever, Richard, very clever.
Thanks – it suggested itself really. It’s a good model, eh?
But why does it have Celle number plates?!
Our neighbour had a mint green Sierra Ghia with rather fetching dark green plastic bumpers. I also remember those Sierra bumpers as being almost impossible to break. They must’ve been hugely thick.
Herewith a Sierra with a red tint to the plastic:
Not a great image, but you can see the green lower plastic against the black upper strip.
Thanks, Robertas, for the Lutz quote. I suppose BMW found that out afterwards. Maybe Lagaay might have been more cautious with his prognostications. Quite a few cars used plastic-oid panels: BX, XM, 307 front wings, maybe the Honda Beat and Suzuki Capuccino and the Espace, long before BMZ’s Z1. Goodness, to read Kacher on the Z1 you’d never imagine the Espace existed.
That said, the ’84 Espace had GRP panels and Xenoy’s advantage is in its robustness and that it can be used in injection moulding. As to time, if you use fewer panels and the car weighs less and if plastic’s cheaper than steel then the time cost can be offset.