Northern Exposure® is a unique thermal barrier technology that recycles the free heat energy for more efficient heating. All four sides of the spa, plus the floor and cover, are lined with copper material to reflect radiant heat energy generated from the pumps back into the spa. Heat is then absorbed by the plumbing and shell to help maintain water temperature. Finally, the entire exterior of the hot tub is wrapped in 3M Thinsulate™ Insulation, the same incredible material utilized in winter clothing. This three-layer patented system ensures energy created by the spa stays in the spa.