nextec epic nylon. it has a very comfortable and soft hand, but it pills like fucking crazy and has rather poor water resistance over the lifetime of the garment.
edit for a bit of backstory: this is the textile used in USSOCOM's PCU level 5 uniform, a design referenced by acr in a few other items. One of the founding fathers of the PCU programme, Mark Twight of gym jones fame, picked it because he emphasises dry time and vapor transmission over pure water resistance. The color "alpha green" is a direct reference to the PCU system, although the color in the acr pictures does not seem to be the same as the one used in the L5 uniform.