SAN FRANCISCO -- PTW Architects, the firm that designed the famed Swim Cube at the Beijing Olympics, considered puttingsolarpanels on top of the building.

The company, though, found that it worked better to dynamically adjust the polymer shell around the building to let in sunlight and heat. The outside of the building is coated with a three-meter thick mesh of pillows from a material called ethylene tetrafloroethylene (ETFE) that can be inflated or deflated to let in light, or deflect glare.

"The ETFE pillows were more efficient in saving energy than what could have been done by putting PV panels on the roof," said John Bilmon, managing director at PTW.

In all, the design of the building cut power by 35 percent. A good portion of that came from letting sunlight in naturally to heat the water.

Other fun Swim Cube facts: The building is square to order to compliment the round Bird's Nest stadium nearby. Square buildings represent earth while round ones represent heaven. The blue color also complimented the red stadium.

In all, the building was made from 22,000 steel beams, each one different from any other. Although the building was a straight square, none of the beams run along conventional straight lines. "The beams never ever followed straight lines," he said. The beams were connected by sticking them in, Tinkertoy-like, into 1.5 meter wide steel nodes. The firm was going to assemble these structures at the factory but found it was cheaper to just hire people on site to do it.

The firm studied bubbles extensively to come up with the shell. Bubble studies can be traced back to Lord Kelvin, who noted that bubbles are round when exposed to air but connect to each other through flat surfaces. Kelvin designed 12 and 14 sided polygons to demonstrate how bubbles efficiently fit together.