What components make up a typical insulating glass unit and what does the nomenclature associated with it mean?
Here in a cut away unit is the answer.

Following the labeling in Fig. 1, the exterior ply is the outside lite of glass and the interior ply in the inside piece of glass.

When discussing coatings, the surface where the coating is applied is referenced quite frequently. As shown, the outboard lite of glass has surfaces #1 and #2, and the inside piece of glass contains the other two surfaces. The numbering starts with the surface of glass which is exposed to the outside, #1, and ends with the side of the glass which is on the inside, #4.

The unit shown is a dual-seal unit (primary and secondary) and the desiccant is located inside the frame to absorb moisture.

USG
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