The linear thermal expansion coefficients of oriented films of poly(p-phenylene-2,5-didodecyloxy-terephthalate) in the three structures B, A, and L(f) are reported. The results are interpreted in terms of a molecular laminate model in which the rigid main-chain layers are separated by the aliphatic side chains. In a film oriented unidirectionally the rigid main-chain layers provide a negative contribution to the thermal expansion coefficient, while the side chains supply a positive contribution. Therefore, the resulting expansion coefficient alpha depends on the details of the main- and side-chain packing and low-temperature values between alpha = +0.3 X 10(-5) K-1 (A and L(f)) and alpha = -1.2 X 10(-5) K-1 (B) are found in highly oriented films. Measurements on undrawn films are in accordance with the molecular laminate model.