An IGU must be a complete, factory-sealed assembly with the spacer and gas fill already in place at the time of importation. Glass panes imported separately — even if intended for later assembly into an IGU — classify under the appropriate flat-glass heading (7005 or 7007) rather than 7008. CBP may request manufacturing or quality-control documentation confirming the sealed-unit construction if the assembly status is not evident from the physical goods.

Yes. Heading 7008 covers multiple-walled insulating units regardless of whether the individual glass plies are annealed, tempered, or laminated. Once the panes are assembled into a sealed insulating unit, the unit as a whole classifies under 7008 rather than under 7007 for the safety-glass component. This is a common classification question for high-performance window units that combine low-e coatings, laminated inner panes, and gas fills.