Building Regulations and Window Energy Ratings
2) Get your IG components list
When considering either using a pre-registered or registering for a new WER, IG manufacturers will be required to supply the installer/fabricator with a list of components that they are able to include within sealed units to meet WER requirements. The IG manufacturer should indicate preferred products and dimensions. E.g. Spacers such as Aluminium or Warm edge bars such as Thermobar and Thermoflex; sealants such as Isomelt Hot Melt or silicone sealants (sealant type not brand must be named); and types and brands of glass that can be supplied within their EN1279 scope.
Note: Hot Melt has a significantly lower conductivity value than PS and PU.
Building Regulations and WERs Page 8