In their 2006 paper Christiansen et al. describe the "stuffed Whipple shield" wall of the ISS's Destiny Module. The outer skin, the Whipple shield's "bumper" layer, is a thin layer of aluminum (alloy 6061-T7). Inside that is the "stuffing" (appropriate for a Thanksgiving question! ;-) layers of Kevlar fabric, Nextel fabric, and multi-layer insulation (MLI). The innermost layer is another aluminum layer (alloy 2219-T87 for this layer, slightly denser than the 6061-T7) that serves as both the pressure vessel wall and for the inner layer of the Whipple shield. Its thickness is given as 4.8 mm.
Question: for that inner layer, which of the two functions, either withstanding the internal atmospheric pressure or providing sufficient areal mass density for the Whipple shield, set that thickness?