The Wave Core™ technology used by THERM-A-REST is a method of specially arranging and constructing material in such a way as to minimize heat lost through thermal conduction between the body and the ground beneath us. It involves a simple layer of horizontally arranged waves. This simple structure doubles the thermal insulation compared to a regular air mattress with no insulation. And all this without the weight and bulkiness of additional fibers or the need to fill the mentioned product with heavy insulating material.
A good idea, modern materials, yet still a simple shape, is sometimes more than the most complicated down fillings.
It is a top-notch and perfect choice, or literally warm and luxurious sleeping for three seasons of the year (winter and any sleeping somewhere in the mountains will of course require something better).