The Arxx reFit basement finishing system increases energy efficiency and reduces costs. The system results in a R-value for the finished wall assembly, which provides thermal resistance and reduces air exchanges to keep indoor temperatures constant. It is also resistant to mold, mildew, and rot. reFit comprises lightweight high R-value vertically interlocking insulation panels that are drywall-ready with wall clips and adjustable shims. It requires no additional vapor barrier and has embedded attachment strips for installation of interior finishes. The panels don’t off-gas and they emit no CFCs, HCFCs, or VOCs. They are made of expanded polystyrene.