Apparel permeability is most frequently measured by controlled air flow through fabric. Values recorded for this test are cubic feet of air per square foot of fabric for 1 minute of time or volumetric flow rate. Vascular grafts are not tested using air flow, but rather liquid flow measurements. Fluid volumetric flow is recorded as milliliter of fluid per square centimeter of fabric per minute. To measure meaningful values of vascular graft permeability, a controlled pressure must be maintained across the fabric surface.