An insulating glazing includes at least two substantially parallel glass sheets, which are spaced apart by at least one air- or gas-filled cavity forming a cavity internal to the glazing, a spacer, which is arranged at a periphery of the glass sheets and which keeps the two glass sheets spaced apart, and an adhesive bonding system arranged to fasten the spacer to each glass sheet via two of opposite fastening faces of the spacer, wherein the spacer includes, at least for one side of the glazing, a mirror-function reflective surface on an internal face of the spacer facing the internal cavity of the glazing.