A name for polyethylene terephthalate (PET) developed by E.I. Dupont de Nemours&Co (Inc.). A film base material exhibiting superior strength and tear characteristics.
Cronar is the trade name for Dupont motion picture products; ESTAR Base is the trade name for Kodak products.
Polyester when used as a film base has the same requisite properties as nitrate and acetate base: it is fully transparent, and is elastic. Besides, it has greater tensile strength. Compared to other bases it has decisive advantages: it is unaffected by temperature changes or humidity and does not release harmful gases. Polyester could therefore be the ideal base for cinematograph film.
Unfortunately, the coating of the light-sensitive emulsion on the polyester base is more difficult. Therefore polyester base was previously used mostly for 8mm film and for 16mm release prints. Nowadays it is also used for 35mm films. Despite all the advantages of polyester one should bear in mind that in the final analysis the life-span of a cine film is determined by the life-span of the recordings made on the light-sensitive emulsions and these are in any case shorter than the life-span of polyester. 1
It has now been accepted that Polyester is also, to some degree, subject to the decomposition manifested by the vinegar syndrome process.
1 FIAF, 1986, Preservation and Restoration of Moving Images and Sound, Federation Internationale des Archives du Film, FIAF, Brussels, Belgium