Like hikers, electricity in a circuit, and water flowing downhill, airborne vapors also take the path of least resistance. Therefore, it is important to maintain proper orientation with a sorbent tube while air sampling. If the sorbent tube is placed in a horizontal position, “channeling” may occur due to the sorbent falling away from the walls of the glass sorbent tube. As the vapors take the path of least resistance (i.e. through the “channel”), the effectiveness of the adsorption by the sorbent bed will be decreased because of the effective surface area being diminished. The sorbent tube should be maintained in a vertical position (or as close as possible) to avoid the “channeling” effect.