This vacuum form mold is made of a porous aluminum product that eliminates the necessity for drilled vacuum holes. The mold shown here could be a complete vacuum form mold but it has a great deal of detail which is difficult to form with vacuum only. So in this particular case, there is another half that is not shown that provides air pressure on the opposite side of the sheet to provide sufficient differential pressure to form all details of the finished part.
Figure 1 shows the computer model of the vacuum side of the mold. Figure 2 shows the actual mold just before shipment.