The coefficient of thermal expansion (CTE) is an important property of materials. If the material is to be exposed to temperature gradients in its lifetime, it is often important to determine how much it will expand or contract over the temperature range. This application note details the method to determine the expansion coefficient of two polymers mounted in the PerkinElmer® DMA 8000 in tension mode. The methodology is relatively simple and this approach has been shown to give accurate expansion coefficients. These experiments are often referred to as being run in the “TMA mode” because the DMA 8000 is being used as a TMA in these cases.