to that angle or an even greater rotation angle may be permitted referring to fig7 it can be seen that from the front of the insulative window assembly 2 i e the left hand side of the illustration of fig7 each slat 4 anteriorly overhangs or overlaps the adjacent subjacent slat 4 the ridges 18 42 disposed on opposed longitudinal edges 6 of slats 4 mate with each other when closed as shown in fig7 to provide the overhang overlap in other exemplary embodiments the respective longitudinal edges 6 of slats 4 may include other protuberances in one edge that mates with or is received within a channel or other receiving member in the opposed edge for example a rib flange or fin may be used in conjunction with a corresponding ridge groove or other cavity or indentation in yet another embodiment each slat 4 may be generally flat with opposed surfaces that curve toward each other and converge to form a tip at longitudinal edges 6 according to this exemplary embodiment the thickness of slat 4 tapers near longitudinal edges 6 and respective longitudinal edges 6 of adjacent slats 4 may overlap when slats 4 are in closed position another possibility is a squared u201c s u201d shape in cross section where the upper edge of each lower slate hooks with the lower edge of the next upper slat and so on the.