Alpen Energy Group. Alpenglass windows use a combination of low-E coatings; suspended Heat Mirror films; gas fills; vinyl, wood, or insulated fiberglass frames; and low-conductivity spacers to achieve whole-unit U-factors as low as 0.10 for fixed units and 0.14 for casements using superinsulating glazing combinations, such as triple films and xenon gas, and superinsulated frames. Depending on the customer’s requirements, the manufacturer can provide products with higher SHGC values for passive solar gain, or whole-unit SHGC values as low as 0.15. 800.882.4466.