Universal vacuum cups are like flat vacuum cups except they have no bottom cleats.
As a result, deflection is higher than flat vacuum cups and the cup area exposed to vacuum becomes smaller as vacuum level deepens and the cup lips flatten out.
Under a heavy pull, a universal vacuum cup will “tent” up and the effective vacuum area will increase until it equals that of a flat vacuum cup, at which point, it will have similar load capacity.
Thin workpiece materials can be drawn in toward the cup center and essentially seal of vacuum from the universal vacuum cup lips so that the effective area becomes so small that the cup cannot pick up the workpiece safely.
Universal vacuum cups have very little angular compensation ability so they should always pick up perpendicular to a flat workpiece surface.