Data from the Thermal Emission Spectrometer (TES) on board the Mars Global Surveyor spacecraft are used to analyze the structure of and materials comprising crater-related wind streaks. Comparisons of high-resolution TES albedo and TES-based thermal inertia values within and adjacent to the streaks allow us to constrain the properties of the streaks and gain insight into their physical structure. The majority of the analyzed Type I bright, depositional streaks are distinct from the surrounding terrain in albedo, but not in thermal inertia. We conclude that these streaks consist of thin deposits of bright material greater than ~1 μm thick but less than 1--3 mm thick. The majority of the analyzed Type I dark, erosional streaks identified from Viking images are now indistinct from the surrounding terrain in both albedo and thermal inertia. We conclude that these streaks have been covered by a thin deposit of bright material greater than ~1 μm thick but less than 1--3 mm thick. All of the analyzed Type II dark, depositional streaks are distinct from the surrounding terrain in both albedo and thermal inertia. We conclude that these streaks consist of deposits greater than a few centimeters thick. In this case we were also able to use the thermal inertia values to estimate the particle sizes of the deposited material; the values correspond to a broad range of sand-sized particles easily mobilized by wind, supporting the deflation/deposition theory of Type II streak formation. ¿ 2001 American Geophysical Union