Publisher Summary This chapter discusses the results of weathering exposure of chlorinate polyethylene elastomer. Dow Chemical Company Tyrin® chlorinated polyethylene elastomer is often used as a modifier for PVC. Sunlight, ozone, and oxygen can commonly cause environmental degradation of many elastomers by attacking both saturated and (especially) unsaturated sites along the polymer chain. Because Tyrin products have a saturated molecular backbone, they are not as susceptible to such attacks as are many other elastomers. Long-term exposures of properly formulated rubbers made with Tyrin elastomers have shown no cracking when tested in an ozone atmosphere or when exposed to outdoor weathering.