Hemp would make a great binder also in a conglomerant type infill. Another product that occured to me is using solid wood as in fill. The log cabin industry for years has been claiming (and proving) wood is a good insulator and provides thermal mass (stores heat). How about block wood laid in using hemp or wool as chinking layered between coarses. Low grade and cull wood could be used , soft pourous spec. would probably provide the best r values.
