Chemical stability is a key concern for materials used in medical applications. Many different mechanisms can be responsible for changes in mechanical properties of polymers due to exposure to a chemical environment. Environmental stress cracking (ESC) is the most important mechanism for thermoplastics used in medical devices.

In addition to affecting aesthetics, the stress cracking can seriously compromise mechanical integrity. The proper selection of a medical plastic requires a thorough analysis and interpretation of chemical stability. Copolyesters have been shown to retain their mechanical properties after exposure to chemicals such as isopropanol and lipid solution.