The Pelican Case Pressure Equalization Valve is a simple device.  It consists of a housing with a hole through it that is covered with a thin Gore-Tex® membrane.  According to the Gore™ tech sheet: “The microporous expanded polytetraflouroethylene (ePTFE) membrane continuously allows the free passage of gases and vapors, equalizing the pressure differential between the enclosure and ambient before it builds to the point that a seal is compromised.  Water, dust and dirt are repelled by the hydrophobic membrane, thereby protecting expensive and sensitive electronics.” Trust only Genuine Pelican cases to house your valued equipment.