Abstract: An architectural insulating glass unit with an insert in the airspace is disclosed The IGU comprises two glass facings; an open cell honeycomb insert sized to be positioned between the two glass facings in the insulating glass unit; and a perimeter spacer dimensioned to secure the two glass facings and the open cell honeycomb in the insulating glass unit, wherein the open cell honeycomb insert is between the two glass facings. In one embodiment, the open cell honeycomb insert is constructed from polycarbonate tubular honeycomb. In another embodiment, the open cell honeycomb insert is regular. In the preferred embodiment, the open cell honeycomb insert is constructed from regular polycarbonate tubular honeycomb. A method for preparing the insert is also disclosed.