Bales of straw are also natural and inexpensive, and they provide excellent insulation. This makes straw-bale construction an economical green-building method. Since straw is a byproduct of grain farming, it often goes to waste, so using it in construction is a great way to reuse it.
Straw-bale construction is versatile, too. Since you're using the straw bales either to construct the frame or as insulation in conjunction with a wooden frame, the house itself can look however you want. And no big bad wolf is going to blow down this house of straw -- in most straw-bale construction, recycled steel beams or bamboo rods support the bales.