Andersen Windows. Low-E4 glazing, now standard on all 400 Series windows, is a dual-pane system layered with 11 microscopic coatings and filled with argon gas for a center-of-glass SHGC range from 0.41 to 0.44 and a U-factor range of 0.27 to 0.28. The vinyl-clad 400 Series casement without grilles and with Low-E4 glazing has a whole-unit U-factor of 0.30 and an SHGC of 0.34. Frames are primarily vinyl-clad wood, but some products include components made from composite or glass fiber. The glazing incorporates a sunlight-activated exterior coating that reduces dirt buildup and water spots, the maker says. The windows are Energy Star– and Green Seal–certified. 800.426.4261.