The susceptibility of spacecraft materials to HCl exposure was investigated in light of concerns to potential contamination during evolved expendable launch vehicle (EELV) overflight scenarios. Overflight refers to the circumstance where one spacecraft, resident on a launch pad, may be exposed to HCl generated from an earlier solid rocket launch at an adjacent pad. One aspect of the overflight risk assessments involves spacecraft materials susceptibility to HCl exposure. This study examined a wide range of spacecraft materials after being exposed to HCl vapor in a well-characterized facility. Sample thermal/optical and electrostatic dissipation properties, as well as surface chemical and morphological features, were characterized before and after the HCl exposure. All materials tested, except for indium tin oxide (ITO) coated Kapton film, showed no significant degradation after HCl exposure of up to 4800 ppb-hr. The ITO coated Kapton sample showed slight signs of degradation after being exposed to 500 ppb-hr HCl, as the surface resistance was increased by a factor of 5. However, the potential HCl dose inside the payload fairing (PLF) was estimated to be far below 500 ppb-hr in an EELV overflight event. These results, along with other relevant laboratory test data on the HCl removal efficiency of the filtration media used on the launch sites, provide the technical rationale that properly filtered air as the PLF purge should pose little risk in terms of HCl contamination under EELV overflight scenarios.