Our A Rated glass is made up of a 4mm Float as well as a 4mm clear but is made up with a super spacer-argon filled. Meaning there is no chance of any heat loss through the units. Super Spacer introduces no-metal warm edge technology to windows, helping to deliver windows of the highest standards. Warm edge spacer bars are made of materials which are more thermally efficient than metal. It has a u-value of 1.4w/m2K meaning this unit will ensure to keep warmth and comfort inside your home.