This is a concern for highly valuable, highly vulnerable, highly used film images. The plastic sleeves protect the film surface. For prevention of moisture build-up on the surface of the film in cold storage during changing climate conditions. The use of plastic sleeves inside paper enclosures is necessary when transporting film images to and from cold storage vaults or in the case of humidity elevation in the vault. The lower the temperature, the slower the rate of deterioration.
Cold storage slows deterioration more, especially for color dye images.
All color film, both positive and negative, needs to be stored in cold storage. Color dyes are unstable and will fade unless stored in cold storage. Cold storage will preserve color images indefinitely. A difficult determination may have to be made as to whether or not a certain collection is of high enough value or rarity or if it is used extensively enough to deserve the extra cost of the plastic sleeves.