Sufficient data are available from studies of urethan foams and elastomers to draw semiquantitative conclusions regarding the effect of any gross structural change on most polymer properties. These relationships apply to other areas of application as well, e.g., coatings, adhesives and sealants. Future research may be expected to provide more reliable control of the many reactions involved in preparing urethans, thus better control over structure. Similarly a more quantitative and extensive knowledge of polymer properties may be expected. The result of these combined efforts will be a more precise knowledge of structure-property relationships and an improved ability to produce polymers having the properties desired for a wide range of applications.