For fenestration the window and door types, as well as TDL (true divided lite) and SDL (simulated divided lite) combinations, contribute to the overall balance of the ratings.
Each product type is individually tested. Swing products tend to rate better than sliding or folding products. The breakups of the glass have the largest impact. The TDL rates lower than the SDL. TDL breakups have more thermal transfer because the muntins and bars break the glass into individual pieces and the thermal mass of the muntin and the glass spacer edges produce lower efficiency. SDL divided lites give a similar appearance as TDL yet they rate better because the divided lite elements do not break up the glass. As a result the SDL has better efficiency ratings as a result.
The TDL appearance is an important design element and it also can improve overall weight of glass by having smaller square footages per lite and thinner glass pane requirements. Weighing the different advantages of each product type requires a balanced approach during the design phase of the building.