An exterior insulation and finish system (EIFS) has many virtues as an exterior cladding system for residential and commercial structures. One such virtue is its ability to offer a wide variety of durable exterior finishes that serve an aesthetic and protective function. The U.S. EIFS industry now has available a proven history of performance that spans three decades in EIFS applications. The performance differences among various chemistries and formulation options are now better understood, enabling more informed choices with respect to cost performance tradeoffs. Although new developments in EIFS technology are continually being implemented and needs for sustainability and long-term durable energy-efficient systems continue to increase, having valid test methods that can predict long-term performance is a valuable commodity. With more than three decades of external test results for EIFS finishes now in hand, the value of individual internal lab tests can be examined, and their correlation with external results can be assessed. The term durability can have a broad definition. It is typically not characterized by a single test but is a comprehensive assessment based on several tests. Properly developed and interpreted, lab tests can be used to estimate long-term durability performance. This paper focuses on various lab tests that can be used to forecast exterior performance. It also explores various aspects of polymer chemistry and formulation and characterizes their effects on the exterior longevity of EIFS.