A Quaker School in Maryland looks like a regular building on the outside. The surprise is inside the walls.

Straw from nearby fields has been baled and stacked inside the exterior walls, providing a natural and superior insulation that's earth-friendly.

Mike Furbish built this school. His own home outside Baltimore, Maryland is made of straw bale.

He likes this form of green building because straw bale doesn't require any manufacturing and doesn't create toxins or waste.

So how does it work?

The headmaster of the Friends Community School explains the straw bale is placed in the walls like normal insulation. But unlike the fiberglass stuff, straw bale is so efficient it has an insulation rating of 48 -- way above typical building codes.

Once the bales are stacked, they're covered with an adobe-type mud mixed on the premises that will provide an airtight seal.

The Quakers have always been earth-friendly. Stewardship is one of their religious tenets, and they have been out in front when it comes to green building. The philosophy: Conservation creates harmony.

Friends Community School is green beyond its walls. It's oriented on the land and curved so it can follow the arc of the sun and get light all day long, a technique called passive solar.

It will have a green roof, waterless urinals, and radiant floor heating (which uses less energy). The students will maintain the surrounding wetlands, and during construction, the debris is being carefully sorted and recycled.

Straw bale construction isn't new. It's been around for more than a century, mostly in the West and Midwest.

In Europe, there are straw bale homes that have been around more than 200 years. Talk about sustainable!

The Department of Energy Web site recommends straw bale construction, calling it practical and structurally sound.

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