In this paper, the in-plane linear coefficients of thermal expansion (CTE) (alpha x and alpha y) of a newly developed family of all aromatic and aromatic/aliphatic copolyester thermoset films prepared from spin coating were measured. The volumetric CTEs (beta) were determined by a Pressure-Volume-Temperature (PVT) technique (1). Based on the difference between the volumetric CTEs and the sum of the in-plane linear CTEs, the out-of-plane linear CTEs (alpha z) were calculated. The effects of film processing, including film coating and curing, on the CTEs are discussed. It was found that the linear CTEs varied significantly with the processing conditions, the volumetric CTEs were essentially constant, and the out-of-plane linear CTEs (alpha z) of the spin coated films were higher than the in-plane linear CTEs (alpha x,y).