An epitome of data obtained in the Research Laboratories of Tennessee Eastman Company on the structure and properties of polymers and fibers of poly (1,4-cyclohex ylenedimethylene terephthalate) is reported. Special attention is given to the effect on properties of varying the proportion of cis and trans isomers of the 1,4-cyclohexanedi methanol used in making the polymers. Solubility, density, and those properties of polymers that are associated with temperature are affected by the cis/trans ratio, but the tensile properties of fibers and fabrics are not. The conformational forms in which these isomers might occur are considered. The crystal structures, deduced from x-ray diffraction data, are unusual in that the crystal lattice in polymer composed wholly of either isomer is distorted by addition to the polymer of an appreciable proportion of the other isomer. Melting point data show no evidence for the existence of a eutectic composition. Kodel polyester fiber is at present manufactured of polymer in which the ratio of trans and cis isomers is approximately 2 to 1. This fiber has a very low degree of susceptibility to water. It is also highly resilient at room and laundering tempera tures, whether wet or dry. These factors probably account for its excellent behavior in wash-and-wear fabrics.