Precast concrete sandwich panels are comprised of a thinner precast outside skin (typically 70–80 mm) and a thicker precast structural inside section (typically 100 mm), which are held together by non-thermally-conductive ties, with an insulation layer in between.
The system allows the outside skin to expand and contract with fluctuations in temperature, without compromising the structural effectiveness of the building. It also maximizes thermal mass benefits by having the large volume of unlined painted concrete on the inside of the building. The high quality of the precast finish means both surfaces can be stained or painted.
In buildings that employ passive solar design, winter sun enters through north-facing windows and is absorbed into the high thermal mass interior walls. At night, when the sun goes down and temperatures drop, that same heat is released slowly back into the interior of the building.