For all who have been searching for attractive, energy-efficient, high-performance vinyl windows, let us clear the way. The Endure™ Window Series has been independently tested to meet strict energy efficiency standards and is ENERGY STAR® certified. Endure brand windows come standard with the highest-quality frame and sash designs and ComforTech™ Warm Edge Glazing, a high-tech glass package that measurably improves thermal performance—for less heat loss, warmer glass temperatures and reduced interior condensation.