Air filter for intake hose on compressor. A saturated filter allows moisture to penetrate directly into the compressor, especially when the temperature drops to freezing in winter and condensation forms. The location of the filter is particularly vulnerable on Tesla X. You can read more about this here.
Tesla started using this type of air filter on the production line in the fall of 2016, as far as we understand. You can also buy the air filter with hoses directly from Tesla (part number 1027931-00-B for Tesla X, price approxm. price approxm 18 EUR., 1061821-00-B for Tesla S, price approxm. 27 EUR).