Humidity buffering refers to the ability of materials to moderate changes in relative humidity

Relative humidity

Relative humidity is a term used to describe the amount of water vapor in a mixture of air and water vapor. It is defined as the partial pressure of water vapor in the air-water mixture, given as a percentage of the saturated vapor pressure under those conditions...

 by absorbing and desorbing water vapour from surrounding air. This is also referred to as moisture buffering.

The phenomenon has long been exploited for preserving items from damage that could be caused by either excessively moist or dry conditions.

Examples

1. Cigars are usually kept in a wooden box called a humidor

Humidor

A humidor is any kind of box or room with constant humidity, and ideal temperature, used to store cigars, cigarettes, or pipe tobacco. For private use, small wooden or acrylic glass humidor boxes for a few dozen cigars are used, while cigar shops may have walk-in humidors, sometimes consisting of a...

. A pan of water is placed in the humidor

Humidor

A humidor is any kind of box or room with constant humidity, and ideal temperature, used to store cigars, cigarettes, or pipe tobacco. For private use, small wooden or acrylic glass humidor boxes for a few dozen cigars are used, while cigar shops may have walk-in humidors, sometimes consisting of a...

 so that the wood will absorb water vapor at close to 100% Relative Humidity

Relative humidity

Relative humidity is a term used to describe the amount of water vapor in a mixture of air and water vapor. It is defined as the partial pressure of water vapor in the air-water mixture, given as a percentage of the saturated vapor pressure under those conditions...

. It is then used to store the cigars at fairly constant relative humidity, between 45-50%.

2. Silica Gel

Silica gel

Silica gel is a granular, vitreous, porous form of silica made synthetically from sodium silicate. Despite its name, silica gel is a solid. It is a naturally occurring mineral that is purified and processed into either granular or beaded form...

 is widely used in the opposite way, as a desiccant

Desiccant

A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its local vicinity in a moderately well-sealed container....

 to buffer relative humidity inside museum display cases, packaged clothing, electronics and anything that might be damaged by condensation.

Recently, there has been an interest in the field of building science

Building science

Building science is the collection of scientific knowledge that focuses on the analysis and control of the physical phenomena affecting buildings. It traditionally includes the detailed analysis of building materials and building envelope systems...

 and architecture

Architecture

Architecture is both the process and product of planning, designing and construction. Architectural works, in the material form of buildings, are often perceived as cultural and political symbols and as works of art...

 in using humidity buffering as a passive indoor climate control, thus reducing the need for air conditioning

Air conditioning

An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...

  and ventilation

Ventilation (architecture)

Ventilating is the process of "changing" or replacing air in any space to provide high indoor air quality...

.