Thanks, FW. Here is what I found on the manufacturer's website:
The “Batting a Thousand” Natural Turf (B1K) is a dual fiber system comprised of Shaw’ high-performance Strenexe® XD slit film and Shaw’s Bolt® monofilament. This system provides high durability and functionality by preventing the infill from “splashing,” maintaining adequate infill levels across the field. The Bolt fiber provides excellent ball roll, friction and natural grass aesthetics, ensuring that the playing surface at Chase Field will appear nearly identical to that which has been in place since the stadium opened in 1998, including the dirt path between the mound and home plate.