A venting configuration sufficent to vent the vehicle at launch an assure pressures between blanket layers below 5x10 -5 Torr in space. The princple that MLI works on is that radiative heat transfer between the layers predominates over conductive or convective transfer. Torr was required before effective blanket insulation was achieved. Figure 3. shows a plot of heat transfer vs pressure. At 1x10 -4 Torr there is a factor of two increase in heat loss.
Torr is small.
Thermal Design Principles of Spacecraft and Entry Bodies, ed.