GIRARDOT, Colombia — Forget steel and concrete. The building material of choice for the 21st century just might be bamboo.

This hollow-stemmed grass isn't just for flimsy tropical huts anymore — it's getting outsized attention in the world of serious architecture. From Hawai'i to Vietnam, it's used to build everything from luxury homes and holiday resorts to churches and bridges.

Boosters call it "vegetal steel," with clear environmental appeal. Lighter than steel but five times stronger than concrete, bamboo is native to every continent except Europe and Antarctica.

And unlike slow-to-harvest timber, bamboo's woody stalks can shoot up several feet a day, absorbing four times as much world-warming carbon dioxide.

"The relationship to weight and resistance is the best in the world. Anything built with steel, I can do in bamboo faster and just as cheaply," said Colombian architect Simon Velez, who almost single-handedly thrust to the vanguard of design a material previously associated with woven mats and Andean pan pipes.

Velez created the largest bamboo structure ever built: The 55,200-square-foot Nomadic Museum, a temporary building that recently debuted in Mexico City and takes up half of the Zocalo, Latin America's largest plaza.

The museum, open until May, is the brainchild of Canadian artist Gregory Colbert, who wanted a monumental structure built entirely of renewable resources to house his tapestry-sized photos of humans interacting in dreamlike sequence with animals.

He turned to Velez, who two decades ago made a simple discovery.

By using small amounts of bolted mortar at the joints — instead of traditional lashing methods with vines or rope — he was able for the first time to fully leverage the natural strength and flexibility of guadua, a thick Colombian bamboo, to build cathedral-like vaults and 28-foot cantilever roofs capable of supporting 11 tons.

Curing the stalks with a borax-based solution deterred termites.

He perfected his technique on hundreds of projects, mostly in Colombia but also in Brazil, India and Germany with structures as graceful as they are muscular.

In steamy Girardot, a two-hour drive from his bamboo home in Bogota, the 58-year-old Velez has just completed a prototype of an energy-saving store for French retail giant Carrefour.

The 21,500-square-feet structure has a domed roof made of guadua — instead of sunabsorbing metal — that will cut down on air-conditioning costs. In Bali, German Joerg Stamm applied the same technique — learned as an apprentice to Velez — in constructing a 160-foot bridge strong enough to hold a truck.

But Velez, the son and grandson of architects who grew up in a Bauhaus-inspired glass house in western Colombia, has little patience for environmentalists now drawn to his work for its planet-saving possibilities.

"I hate environmentalists. Like all fundamentalists, they just want to save the world," he says.

For this iconoclast who designs exclusively in freehand, bamboo is foremost a high-tech material.

Seismic testing of bamboo seems to back his claim. After years developing construction codes for bamboo in his lab in the Netherlands, Jules Janssen was in Costa Rica in 1991 when a deadly 7.7 magnitude earthquake struck. Touring the epicenter hours later, he found every brick and concrete building had collapsed.

"But 20 bamboo structures built there by coincidence held up marvelously. There wasn't a single crack," said Janssen, a civil engineer and expert on bamboo's physical properties.

In an age of diminishing resources and burgeoning populations, bamboo's environmental and social benefits are its biggest selling point as construction material.

Unlike steel, which is produced in only a handful of industrialized nations, more than 1,100 bamboo species — a few dozen of them suitable for building — proliferate in the tropics. Culms, or stalks, shoot up almost anywhere, easing carbon dioxide's choke on the planet while absorbing water as efficiently as a desert cactus.

But building with bamboo is labor intensive and can be costly in parts of the world, depending on local supply.

Velez estimates that 80 percent of his costs on any project go to paying the 300 specialized craftsmen who follow him around the world, most recently to Guangdong province, China, where he built the country's first commercial bamboo project, the award-winning Crosswaters Ecolodge for tourism.

Bamboo's abundance is, ironically, an obstacle to wider acceptance. Its most visible use is as rickety, makeshift housing — feeding the stereotype that it is poor man's lumber.

That hasn't stopped David Sands. The Maui-based architect creates Robinson Crusoe revival homes in Vietnam, then ships them in panels around the world for quick assembly.

After building a hundred homes in the Islands and a resort in Bali, his Bamboo Technologies company is aiming for the U.S. mainland, where its challenges include insulating against colder temperatures and coping with uninformed building inspectors.

But in a sure sign that bamboo's time may have come, Sands says he's had to turn down a $20 million unsolicited offer for his company from potential investors.

"It came as a total shock. We're not ready for the kind of scale they were proposing," Sands said, laughing.

The world's bamboo crops may not be ready, either — there are few commercial bamboo farms to meet a growing demand, and the United Nations in 2004 warned that as many as half of all wild species may be in danger of extinction due to forest loss.

For the Nomadic Museum, Velez had to ship 9,000 pieces of guadua to Mexico, undercutting much of the material's "grow your own house" mystique.

But shortages may also be filled as bamboo plywood — already a major industry in China — gains acceptance in the U.S. and Europe, and growers rush to meet the demand.

"The rate at which it grows is amazing," says Raul de Villafranca, consultant for Agromod, a Mexican company that is planting 9,880 acres in the southern state of Chiapas. "In one year, you can harvest stalks 15 meters (50 feet) tall, and unlike hardwood, it never needs to be replanted."

San Francisco architect Darrel DeBoer, who specializes in sustainable materials, says bamboo-framed structures buttressed by earth or straw bale are viable in any climate, once isolated from the elements with a proper foundation.

But he says bamboo has the potential to make its greatest impact where its already found.

"If you can afford the high price of land in the states, you're not going to worry about using low-cost building materials," says DeBoer, who has hosted several workshops with Velez. "In contrast, the developing countries around the tropics need affordable housing, and the jobs that building with bamboo can generate."