Cupping occurs when the geometry and orientation of the printed part creates a trapped volume of print material between the current layer and the membrane. This situation may have adverse consequences for print quality and accuracy.

Figure 1. Cupping example.
Figure 2. Example of right vs. wrong orientation to prevent cupping.

It is recommended to orient the part in a way that eliminates or minimizes the risk of cupping.

Figure 3. Left - orientation that would cause cupping. Right - Orientation that would NOT cause cupping.