In a number of key IC fabrication steps in-process wafers are sensitive to moisture, oxygen and other airborne molecular contaminants in the air. Nitrogen purge of closed Front Opening Unified Pods (FOUP) have been implemented in many fabs to minimize wafer's exposure to the contaminants (or CDA purge if oxygen is not of concern). As the technology node advances, the need for minimizing the exposure has become even more stringent and in some processes requires FOUP purge while the FOUP door is off on an EFEM loadport. This requirement brings unique challenges to FOUP purge, especially at the front locations near FOUP opening, where EFEM air constantly tries to enter the FOUP. In this paper we present Entegris' latest experimental study on understanding the unique challenges of FOUP door-off purge and the excellent test results of newly designed advanced FOUP with purge flow distribution manifolds (diffusers).