Just to clarify again: “warm edge” refers to insulating glass edge bond with a thermally improved spacer. There is a clear definition of “thermally improved”. It can be found in the relevant international standard for the thermal transmission coefficient of windows, ISO 10077 part 1, as well as in the standard ISO 12631 for the thermal performance of curtain walling. Both standards contain each a chart with linear thermal transmission coefficients Ψ (Psi-values) for spacers made of aluminium and steel and a second chard with lower values for spacers with thermally improved performance. In cases of coubt, the definition helps to decide which chart is the right to use.

According to this definition, spacers made from steel are definitely NOT thermally improved. “Warm edge” does begin with stainless steel spacers. Stainless steel has a considerably lower thermal conductivity compared to aluminium or steel – it’s not for nothing, that the handles of steel cooking pots are often made from stainless steel.

Therefore, it is definitely not ok to praise steel spacers as somehow thermally improved. And by the way: Just the colour black alone does not provide sufficient evidence for a good thermal quality. Lukewarm edge – something like that just does not exist.