To continue the multi-foil discussion(sorry !) and after learning about hemcrete, the following struck me..

Some of the claimed benefits of hemcrete focussed on insulation. Thermal scan images of two identical homes, one built with traditional materials, the other with hemcrete, showed the traditional home leaking heat. The explanation seemed to be that around openings and between floors, the traditional insulation materials tended to leave gaps or sag. Air gaps also encouraged dampness and so thermal bridging. The argument for hemcrete was that, as a rigid packing material it performed significantly better than traditional materials, even at thicknesses that performed averagely in hot box tests.

Sound familiar?

I wonder if the real world benefits of some of the 'newer' insulation materials are simply based upon the fact that they can be installed as a larger continuous surface that resists sagging and thermal bridging due to dampness? Are our traditional builds actually under-performing by some significant margin, allowing 'marginal' new technologies to match their in-situ results? Should our hot box test involve a hot box that more closely resembles an entire room - with all the detailing and openings and other real world issues?