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Important Environmental Factors for Libraries to Consider

A library collection’s life expectancy is most dependent on its environmental conditions. When conditions are sub-par, damage generally occurs slowly, making it easy to go unnoticed. One of the most common forms of damage is mold growth, which first becomes apparent when a collection gains a musty smell. Because cellulose-based materials are vulnerable to several types of mold, humidity control for libraries is an essential step to maintaining an ideal environment. By knowing which environmental factors are crucial to preserving collections, you can take steps to ensure they are within acceptable ranges.

Environmental Factors to Monitor in a Library


Heat accelerates a book’s deterioration, as deterioration rates double with every 18°F increase in temperature. A good temperature for most collections that the public can access is between 68° to 70°. It is important to keep in mind that temperatures that are too low can also cause damage. For example, some types of plastic and organic materials become brittle at cool temperatures.  

Relative Humidity Levels

In addition to maintaining ideal temperatures, humidity control for libraries is just as essential. Relative humidity relates to the amount of water vapor in the air. When a room’s temperature is warm, the air holds more water vapor. Conversely, cold air holds less water vapor, causing increased relative humidity levels and a greater risk of condensation and deterioration. Paper products expand and contract as they absorb and release moisture in the air. Such actions can lead to splitting, warping, cracking, and page deformations, making a stable environment crucial in a library.

Recommended relative humidity levels range between 30 and 50 percent, depending on the archived materials. When relative humidity levels rise above 65 percent, the risk of mold-related damage increases, especially when there is no air movement. As mold grows, it consumes paper and fabric materials, causing them to become weak and eventually collapse. When mold digests cellulose-based materials, it excretes acidic byproducts that further damages, stain, and discolors items in a collection.


Cellulose-based products, such as paper, are photosensitive. Radiation from light—such as ultraviolet rays from the sun—causes structural damage, fades ink, and leads to paper yellowing, bleaching, or darkening. While natural light may be more pleasing to library guests, it is most damaging to collections. Other types of damaging light sources include fluorescent lamps, halogen lamps, and metal halide high-intensity lamps.

Light damage is cumulative by nature and irreversible in regards to library collections. For this reason, light levels should be as low as possible for the shortest amount of time for books in use.   

Air Quality

Pollutants in the form of particulates and gases deteriorate library collections. Particulates, such as soil and dust, disfigure and stain paper products. Gases cause harmful chemical reactions that acidify library materials, causing them to become weak, discolored, and brittle.

Temperature and humidity control for libraries is a fruitful long-term investment. Environmental-related damage occurs slowly. By the time it’s noticeable, it might cost thousands of dollars to restore and deodorize affected pieces. Humidity control solutions, such as the kinds that Polygon custom makes, maintain a library collection’s environment at optimal levels by monitoring and controlling, temperatures and relative humidity levels, as well as filtering the air. Since the solutions run independently from an HVAC system, library guests remain comfortable and archived items stay protected without causing unneeded stress on the heating and cooling system. Get in touch with Polygon today to learn more about how humidity control solutions ensure the longevity of library collections. 

[Photo from Eduardo Merille via CC License 2.0]

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