As polymer suppliers, guaranteeing quality to our customers based only on physical property testing of the resin is not enough. We must ascertain the performance of our products in their intended application and over the intended lifetime. This includes providing an understanding of how a particular product will work and developing evaluation tools to predict performance.This paper describes applications testing done on several polymer systems involving heat aging, stressing and exposure to aggresive environments to which production parts are normally exposed. The results are surprising in that they are not predicted well at all by measurements on standard test bars. The effects of knit lines, scratches and thickness are also determined and related to end use performance.