An evaporative emissions system may include a first passage selectively providing fluid communication between a fuel vapor region of a vehicle fuel reservoir and an engine air intake system, a second passage in fluid communication with the fuel vapor region and ambient air, and a filter assembly. The filter assembly may be impermeable to at least one of oxygen and hydrocarbons and may be located in the second passage between the fuel vapor region and ambient air. The filter assembly may prevent the at least one of oxygen and hydrocarbons from traveling between the fuel vapor region and ambient air.