Polyester can be stored at room temperature and does not need cold storage for preservation. Polyester is also used as an archival enclosure option for materials, such as Mylar and Melinex brand products. While polyester film is stable, the chromogenic dyes found in color negatives on polyester supports are not permanent and may fade rapidly at room temperature. Preventive conservation actions such as environmental monitoring, good storage, and promoting proper handling through staff and user education, will have a lasting, positive impact on the preservation of a collection. Keeping film cold and dry is ideal; however, a cool environment (40 to 60 degrees) is better than room temperature or higher as it will slow down the deterioration process. The best storage conditions for both black & white and color cellulose acetate film are cold (-15° to 4° C/ 5° to 39° F) and dry (30% to 40% relative humidity) environments for cellulose nitrate, cellulose acetate films in both color and black and white, and color on polyester supports. Black and white film on polyester supports may be stored at a temperature of 18º C (65º F) or lower and a relative humidity of 30% to 40%. Freezing film is the ideal temperature to preserve film for the long-term. At freezing temperatures, the natural decomposition of cellulose nitrate and acetate is slowed down. Cold storage is predicted to extend the life of acetate negatives by a factor of ten or more. Three layers of protection are recommended for the storage of film base photographic materials. Negatives and positives should be placed in sleeves or envelopes, which are then placed in a box or drawer, and these boxes or drawers on shelves or in a cabinet. Motion picture film and microfilm should be stored in unsealed containers in cabinets or on shelves. Labels such as acid-free, lignin-free, or buffered do not guarantee that a material is safe to use with photographic materials. Chemically inert papers may be harmful to the photographic image; the only way to be certain of the stability of the paper is to purchase materials that have passed the Photographic Activity Test (PAT). There are also considerations to be made regarding paper or plastic enclosures. Factors such as use, handling, and cost should be considered when selecting archival storage materials. There are several resources provided in the external links section below that can assist with the selection of proper storage materials for photographic materials. Film materials should be stored in interior rooms away from exterior walls and places that do not have extreme temperature fluctuations.