Abstract: An insulating window insert panel provides for vapor and draft barrier functions and also provides for the supporting of a decorative panel or material on the inside surface. The panel is particularly adapted for use with double-hung widows or the like to provide a substantially higher insulating value for the windows so that the heat loss and drafts therethrough may be substantially reduced, and includes a central core or block formed of polystyrene foam which forms a close fit with the window frame and which supports thereon a vapor impervious sheet forming a vapor barrier and a blanket of non-woven fluffy material overlying the vapor barrier sheet for fitting into cracks and crevices and otherwise providing a draft free seal for the window insert, which vapor barrier sheet and blanket are retained at their marginal edges in a circumferential groove and a retaining band carried on the polystyrene core. A decorative panel or sheet may be placed on the inside surface of the window insert unit.