Do you want to build your home out of natural materials? If so, you can build your walls with adobe, cob, cordwood, rammed earth, or wattle-and-daub. Although all of these walls have a long history, their thermal performance is poor. If you want a well-insulated wall, one natural material is the clear winner: straw bales.
A 23-inch-thick straw-bale wall has an R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor.
of about R-33. Moreover, since virtually all straw-bale walls are plastered on both sides, these walls are relatively airtight.