Link: http://adteputek.com/b2evolution/blog2.php/2009/08/22/how-does-vartm-work-and-how-is-porous-pt

VARTM stands for Vacuum Assisted Resin Transfer Molding. It is a composite manufacturing process in which the dry fibers are laid on the tool and vacuum sealed and the resin is drawn through with a vacuum pump. The typical VARTM process is: 1) Dry fabric or a preform is laid up on one-sided tooling 2) Covered with a vacuum bag 3) The air is evacuated by a vacuum pump 4) Liquid resin from an external reservoir is drawn into the component by vacuum 5) The liquid resin is infused into the component 6) A highly permeability resin distribution medium (in this case Porous PTFE Coated Glass Fabric) is placed on the top of the fabric spreads the resin quickly over the lateral extent of the part 7) The resin now only has to flow through the thickness