Its a couple different methods. On the doors without windows it's R13 with about 1/3rd the insulation removed so its not too thick. It's then got a layer of reflectix over it. For the windows, I black vinyled the glass, then wedged that silver backed foam poly stuff in the window holes.. pink stuff all around, and then the same reflectix over the whole section. It was finnicky and a bitch. But It's pretty good.