Three methods for measuring the effects of humidity are described. Method A is a Steady State Test while Methods B and C are Humidity-Temperature Cycling Tests.

Method A imposes a vapor on the material under test that constitutes the force behind moisture migration and penetration. Hygroscopic materials are sensitive to moisture and may deteriorate rapidly under humidity conditions. Absorption of moisture may result in swelling that would destroy functioning utility, and cause loss of physical strength and change in other important mechanical properties. Degradation of optical properties (and of electrical properties in composite devices) may also occur. Although not necessarily intended as a simulated tropical test, this test can, nevertheless, be useful in determining moisture absorption of insulating or covering materials.

Methods B and C obtain their added effectiveness by employment of temperature cycling that provides a breathing action, thereby inducing accelerated corrosion processes and the introduction of moisture into partially sealed devices. This condition imposes a vapor pressure on the device which constitutes the major force behind the moisture migration and penetration.