Side-open builds use resealable tabs or tear-away side seams so the product can be put on without pulling it up over the hips, which suits post-partum use, travel and limited-mobility care. The spec that fails first in the field is tab strength after repeated opening. Ask how many open-and-close cycles the tabs are rated for, and whether the side seam is stitched or ultrasonically bonded.
What an OEM program covers.