If there is an official style of footwear for summer, it is the flip-flop. Those colorful planks of spongy rubber take you to the beach, the pool, or a shady picnic table. And yet these almost-shoes are everywhere in the city, too. Tourists wear them — with their shorts — on the subway. Women wear them to work and change into office-appropriate shoes later. Men wear them with khaki pants to after-work drinks and to bars on the weekend.

All this, despite some facts you don’t need a health expert to point out. Flip-flops expose your unprotected toes to all manner of urban filth. And each time your poorly shod feet hit the cement sidewalk — as opposed to sand or grass — your legs get such a jolt that you might as well be walking barefoot.

But what makes these sandals so attractive is that they connect to the idea of leisure time. Flip-flops are a signifier of one’s preference for casual dress, vacations, and good times. Wearing them in the city is like driving around with a bumper sticker that reads: “I’d rather be at the beach.” And while companies from Louis Vuitton to Old Navy sell flip-flops, the most popular are those that communicate the leisure-time connection the most: Havaianas and Reef.

The Brazilian brand Havaianas — which is in the middle of a major American ad campaign and retail expansion — attracts the stylish urban warrior. “The Havaianas person has fashion sense. They’re young at heart and trend conscious,” the company’s executive vice president, Glen Lagerstrom, said.

Havaianas have been around since 1962, but they weren’t always so chic. Initially created as footwear for the poor, the flip-flops have enjoyed a turnaround in image in the last decade. To celebrate the 1996 World Cup, Havaianas created a series that featured the Brazilian flag, which started showing up here on the feet of those who traveled to South America. Then five years ago, the owner of the brand, Alpargatas, partnered with an American distributor, Style West. The lowly $2 items suddenly ended up in trendy retail outlets and on the feet of celebrities, giving them star power.

The celebrity association comes rather late for a brand that is more than 40 years old. So while it helps that Angelina Jolie wears them, what makes them so suggestive of a sunny lifestyle is the emphasis on color, whimsical design, and that devil-may-care Brazilian flair. “We’re about color, comfort and fun. The style sets them apart,” Mr. Lagerstrom said.

In America, Havaianas now cost between $18 and $22 in stores that range from Macy’s to Ricky’s. The colors range from bright pinks and yellows to blacks and metallics. The most popular style, “Top,” is a simple shape with the brand embossed on the thong. For 2007, the latest model is “Slim,” which is more feminine with a thin strap.

A more masculine counterpart is the Argentinean brand Reef, founded in 1984 by two brothers who were avid surfers. Reef connects to the idea of freedom and leisure through its foundation in surfing culture. Its signature products are the black- or brown-soled flip-flops with repetitive or minimal designs on the tops. At prices from $18 to $45, Reefs are sturdier than the average flip-flops and can stand up to a sporty lifestyle. They’re sold at general retailers such as Bloomingdales, they’re also to be found in sporting good stores, including Eastern Mountain Sports, Equinox stores, and Paragon.

Like Ugg boots, which were originally created as post-surfing footwear, Reef sandals made the jump into mainstream culture. They became a reliable element in the wardrobes of a preppy, well-schooled crowd. Anywhere that tuition costs can lead to cardiac arrest, Reefs are present. Likewise, when those graduates congregate in urban areas, toes are exposed at every given opportunity.

Though Reef and Havaianas are the two most visible brands on sidewalks and subways, they’re generally not found inside offices. For all the attempts at casual Friday, New York has some office standards. Chief among them: Shoes required. Unless you’re running the company or you’re working in a field associated with the Internet (or both), flip-flops don’t fly.

Sure, the West Coast functions differently. And it’s that über-casual Los Angeles aesthetic that New York has, for better or worse, come to adopt. The idea that flip-flops (and, more commonly, jeans) can be worn on almost all occasions came here on a direct flight from LAX. But it works there because an outdoor lifestyle dominates.

If logic prevailed, flip-flops in New York would be relegated to gym showers. But they’re not because, ultimately, we want a piece of that outdoor lifestyle — even if it’s only two slabs of hot pink plastic getting grimier by the minute.

pcatton@nysun.com