'We've never tried to be a fashion item and we've never wanted to be a fashion item,' Bernd Hillen claims, 'It's just that fashion has sometimes found us - and we've welcomed it with a smile.' And yet, as the brand manager of Birkenstock concedes, somehow the German family shoemaking company, established by Konrad Birkenstock in 1896, has found certain of its sandals applauded as fashion icons; familiar - they're affectionately known as 'Birkies' - and yet, contrary to the usual style diktats, easy on the foot, too. 'Why have they become so big? It's simple,' Hillen says. 'They're comfortable. Comfort and functionality are what the company has always been about.'
Indeed, Birkenstock's history and product could hardly be more unfashionable by the standard measures. The company's story lies in orthopaedic footwear; Konrad Birkenstock's big break as a shoemaker came when he was hired by the orthopaedic workshop of the Frankfurt-Friedrichscheim hospital during the First World War to custom-make shoes for wounded soldiers. The hospital director was so impressed that he agreed to sponsor Birkenstock's designs; 10 years later its first commercial product, the so-called Blue Footbed, was launched. Orthopaedic footwear remains its speciality today, as is clearly visible in the unconventional, asymmetric, foot-shaped design of the sandals, with a footbed that supports the foot in the correct way, moulding itself to the wearer over time.
'They have distinctive shape as a consequence of design; its form follows function, and we guess it will take a few more years of evolution before that changes, luckily for the company,' Hillen comments. Certainly the bulbous outline is the polar opposite of sleek, streamlined and often crippling fashion footwear. In fact, almost everything about arguably its most iconic design - the unisex Arizone, launched 40 years ago next and still a bestseller - fights the fashionable, from the brown leather to the two big buckles. Yet it has almost come to define what a classic sandal should look like, and is possibly the only sandal that it is socially acceptable for men to wear.
'Some people love them and some people certainly don't. They won't think these are shoes that are at all sexy,' Hillen says. 'But then we think healthy feet are sexy. Konrad Birkenstock would say "wear fashion shoes as often as you must, but wear comfort shoes as often as you can," even if it's just indoors. Many people wear sandals as a kind of house shoe.'
This, however, might be to waste some serious innovation. Even in its earliest form the Birkenstock footbed was inventive, being made of rubber - roasted, peeled, combed, cleaned and then spun into a stabilising fabric - and cork, for its absorbent and anti-bacterial properties. Then there has been the machinery, all designer by and proprietary to the company, which Birkenstock has developed in order to make its sandals in the best way possible. In 1969, for example, it developed the first electro-mechanical moulding machine, which allowed one adjustable mould to be used to make footbeds of different lengths and widths, all to the correct proportions. It created the first super-lightweight EVA (ethylene vinyl acetate) clog, was one of the first companies to develop more environmentally friendly glue (glue being the chief 'hazard' in shoemaking) and was among the first to develop a line that used no glue at all in its production.
The innovations keep coming, too; recent years have seen solar power adopted to provide 90% of the company's energy needs, with offcuts now recycled to make children's playgrounds and noise-reduction surfaces. 'Innovation saves money, has an environmental benefit - which appeals to consumers more now - and allows us to make new kinds of shoes,' Hillen explains. 'And with Germany's reputation for engineering, the Made in German label appeals internationally, too.'
But can such factors really explain the double-digit-year-on-year growth of a manufacturer of sandals that are at once 'ugly' yet inspiring a dedicated following? Or a brand that is increasingly requested to license its name and so now pondering the launch of its own bags, belts and accessories lines? 'The fact is that people are thinking about their own health more and more,' Hillen offers by way of explanation. 'Even the fashion-conscious customer who wants a pair of our sandals to work with whatever they wear is also much more conscious of looking after themselves. Maybe they just don't want painful feet any more.'