All ALFAPEN uPVC Profiles are with hollow chambers this is one of the reasons that thermal transmission / heat properties of windows is better than those achieved by alternate material.It works excellent for insulation against heat and cold, while reducing the heating and cooling cost to achieve lower fuel / electricity bills. Its perfectly welded corners and three gaskets results in perfect sealing making cooling to remain intact thereby reducing the energy consumption by 30%. ALFAPEN uPVC insulates heat (conforming to ISO 3068).