Dynamic thermal insulation allows passive house (dynamic) U-values with moderate thickness and standard thermal conductivities below 0.050 W/mK. It is a real proof that the race to the best thermal conductivity is useless for buildings.
In short, a small under pressure (5Pa) is created in the space surrounded by the insulation envelope and this induces a small air flow through the permeable insulation. The air, used for ventilation is heated with the heat, leaking away through the insulation. In fact, the thermal insulation acts as large heat exchanger. Passive U-values smaller than 0.1 can be obtained with only 10 cm insulation of 0.040 W/mK. The under pressure is generated by a fan and the heat of the sucked air is stripped with a another heat exchanger in the exhaust of the fan.
Passive housing with moderate thicknesses and totally no building up of moisture (which is easily achieved in passive housing, as demonstrated at the KU Leuven, Belgium) is possible due to the perfect ventilation.
The key is to find a material, which has the right permeability and thermal conductivity. This material should by preference be fiber free and should also allow to build a mechanically stable envelope free from gaps. Indeed, all the air should flow through the thermal insulation. On top of that, it should have a lifetime, exceeding the one of the building.
We think that open celled cellular glass would be an option. This can be done with recycled glass and some foaming agents, which induce crystallization. GLAPOR cellular glass is able to produce 3 x 1.5m boards, which should be ideal to reduce the amount of joints as much as possible. It is also important that foaming agents without any doubt about health are used due to the intimate contact of the ventilation air with the internal foamed glass surface.