Having built in and lived in a cob house (see "Mud and Sticks" I and II <-- those underlined are links) for a couple of years, I am sold on the benefits of clay-based thick walls of high thermal mass. I've been thinking for a long while that the next house I build will be made with double walls and the German light clay straw, but hemp/lime, originally developed in France as IsoChanvre™ might be an equally good choice because of the benefits which accrue to the lime, along with use of a waste product (the hemp hurd). Here's a general overview, though a little dry as videos go:
Another project in Britain:
Here's the first permitted house built in the US, for the mayor of Ashville, NC no less, at about $133/sq.ft.:
A follow up piece on that project provides some more information.
The company which did the above project in the US has done a bunch of the groundwork to give the hemp/lime product the materials testing data and other 'hard data' attributes which help make it more easily salable to building departments (at least in forward-thinking jurisdictions). The lime and hemp materials come premixed and bagged, which is very convenient, and the central distributor for these materials is in Chicago. Good for them! I hope it catches on.
*Sorry about the video formatting being slightly too wide - I tried making various adjustments, but nothing I did seemed to solve the problem. If it is annoying to have the clipped pictures, simply click on through to youTube to see them.