The price of energy and the reduction of CO2 emissions are driving the development of new insulating composites. The variety of Europe's built heritage, with its modenatures, curved facades and architectural singularities, as well as the multiplicity of materials used (adobe, concrete, brick, wood, curtain walling), has led to the development of dedicated insulation composites of very different kinds. Some are cellular with closed pores, some are foams, others are fibrous mats, and others granular "cemented" composites. They are shaped by injection, by compression, or by projection on building site.  Showing the complexity of their microstructures in 3D allows a better understanding of their specificities and the functional properties obtained, such as vapor permeability, fire resistance, etc. X-ray tomography with pixel resolutions of 2 microns and 20 microns is used to first qualitatively describe a straw-based insulator, a glass bead-based insulator, and two silica aerogel composites.
Straw insulation has an uniaxial structure, each strand has a honeycomb structure with radial growth. The textures are circular or ellipsoidal, depending on the local compression ratio. With a resolution of 2 microns, a honeycomb microstructure is perceived, a part of the textures cannot be characterized with this resolution. The glass bead-based insulator shows a multi-scales pore network. With a resolution of 20 microns, the pores are deformed, the contacts between pores are curved, faceted and thick. The triple contact points and pore walls incorporate a much smaller pore network that is highlighted with the 2 microns resolution. The pore walls are indeed made of a foam like material.
Aerogel-based composites include additives, the observed microstructure has more than two phases. The aerogel grains are angular, multi-scales. Their contrast is not homogenous, and some present cracks. Hydraulic binder fills some of those cracks, while organic binder does not.  The contacts between grains are made on full grain faces, which seem to be ‘cemented’ with the binder. Open pores and additions are clearly identified by their morphology or their contrast. 
A quantitative study is then carried out to gain the volume fraction of pore, and the pore size distribution. Homogenization models are revisited to simulate thermal properties and map possible material optimizations. Simulated and measured conductivities are in a 15 to 50 mWm⁻¹K⁻¹ range, covering superinsulation and regular insulation materials. For aerogel-based composite, the volume fraction of low conductivity grains is not sufficient to explain the performance of the materials developed. The drying shrinkage seems to participate in the efficiency of the composites. Simulations show that the volume fraction of fiber or binder required for the elaboration is critical for the performances. The controlled presence of pores between the aerogel grains has little effect on the thermal efficiency. As a conclusion, the rehabilitation of the Tony Garnier city in Lyon with an insulating rendering (FIXIT) shows the deployment of an innovative aerogel composite on a large-scale site.