Abstract: A permeation testing apparatus for determining the permeation of a chemical through a test material. The testing apparatus includes a permeation cell comprising two units, each constructed of a block of relatively chemically inert material which may be placed in intimate contact. One face of each said block has a shallow cylindrical well, that is referred to as the "challenge side". The opposite face of the block has a conical well that is referred to as the "collection side". Two such blocks, or permeation units, are positioned face-to-face ("challenge side" to "collection side") and constitute one permeation cell. The material to be tested is positioned between two permeation units thereby separating the "challenge side" from the "collection side". Four ports are provided perpendicular to the axes of the permeation cell; i.e., an inlet and an exit port for each of the two permeation units. Several permeation units may be stacked, with each interface providing a permeation cell.