the seam 26 the insulating member 30 is inserted between the opposing tabs the insulating member 30 is preferably a strip of continuous nonmetallic low heat conductive material such as rubber the length of the spacer frame bar the tabs 46 of the opposed sides 24 and 25 are subsequently pressed together and closed so as to interlock with each other alternately overlying and underlying one another in an interleaved fashion and separated by the insulating member with careful placement of the insulating member 30 between the alternating tabs 46 metal to metal contact and therefore energy transfer between the first and second sides can be substantially reduced or eliminated fig4 a illustrates an alternate embodiment of a spacer frame bar constructed in accordance with the present invention the spacer frame bar of this embodiment is identical to that of the preferred embodiment save for the construction of its seams 26 in this embodiment the elongate edges 28a and 28b of the first side 24 are untabbed and fiat the elongate edges 29a and 29b of the second side 25 are cut and formed into alternating tabs 46 as described above again each tab 46 is cut to approximately the same size and to substantially the same depth when initially formed the tabs of the second side 25 are aligned to oppose the elongate edges 28 of the first side 24 each tab 46 alternately deflected upward or downward on either side of the edges of the first side in one implementation of this embodiment as shown in fig4 a.