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Lyndon "Duke" Hanson knew he and his partners had hit on something big when the fire marshal at the Fort Lauderdale, Florida, boat show started yelling that the crowd gathered around their Crocs' shoe booth was blocking the aisles. Hanson was tossing pairs of his company's colorful boating shoes at passersby, asking them to slip them on: "People would say, 'Man, those are ugly,' and we would say, 'You just got to try them on.' "

They did, and Hanson sold 1,000 pairs in three days.

That was in late 2002. Last year, Crocs sold 6 million pairs of their spectacularly, well, different-looking casual shoes to teenagers, grandmothers, anyone. The company, based in Niwot, Colorado, outside of Boulder, earned $17 million on sales of $108.6 million. And this February, it raised $239 million in the largest footwear initial public offering ever, suddenly realizing a market value of $1.09 billion.

Lucky? Perhaps. Fashion is like that. Crocs' waterproof clogs and sandals, colorful and iconoclastic, appealed immediately to a certain fun-loving sensibility--giving people, as Hanson says, a sense of cool for being brave enough to wear them in public. And at about $30 a pair, a lot cheaper than traditional boat shoes, they rode a wave that's still building.

But the company understands that fads like this one are wispy and, most of the time, ephemeral, and it has moved swiftly to translate fast fortune into something more lasting. To ensure stability, the founders have bought up not just the factories that make Crocs but also the supplier of the shoes' proprietary resin. They've nailed down distribution with key retailers. And they've focused less on fashion than on sustaining the technology that makes their shoes truly distinctive.

It was Hanson's buddy Scott Seamans, now 52, who sparked Crocs' journey. In 2002, he came across a weird sort of clog developed by Fin Project NA, a Canadian plastics company, for use in day spas. It wasn't just that the shoe looked strange, though it surely did. What grabbed Seamans was the resin, later dubbed Croslite: It was waterproof and lightweight, and, unlike plastics and rubber, it resisted bacteria and fungus.

Even better, the resin softened with body heat to mold to the contour of the foot, providing an unusually comfortable fit, and "circulation nubs" promised to improve circulation and reduce muscle fatigue. Seamans put a strap across the heel and figured the design, featuring holes for air and drainage, would be ideal for boating. While vacationing in the Caribbean, he showed it to Hanson, a former hardware sales executive, and another friend, George Boedecker, who had been an exec at sandwich chain Quiznos. The trio started its company that weekend.

A couple of boat shows later, sales began popping, as buzz traveled first among boaters, then beyond. Crocs "took on some cultural icon status, where people either love it or they think you're the biggest idiot," says Rick Sterling, president of branding consultant Sterling-Rice Group in Boulder. Says Paula Chase, an X-ray technician in Pueblo, Colorado, who sports a pair of navy blue Crocs to work: "They grow on you. Once I wore them, I didn't feel like they were as ugly."