Moisture sorption behavior and dimension change of polymeric materials (ASA, ABS, PMMA, PC, PP, PPS) for automotive exterior lamp has been investigated. The variations of the moisture sorption have been represented following the theoretical model of the Fick's 2nd law of diffusion. In order to understand the dimensional change during the moisture sorption process, the change in length of each sample was studied. The length of polymeric materials increased as equilibrium water content increased. The moisture absorbed polymer materials provided a 33% decrement of the coefficient of thermal expansion, seemingly by swelling the polymer materials under atmosphere condition.

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