5.11's TDU shirt gets Rapid Assault designation because the company says it's the ultimate upper wear for tactical use and battle. A fast-drying, lightweight poly/cotton/spandex knit comprises the body's fabric to wick away perspiration when temperatures and activity levels rise. Side mesh panels also help with ventilation and cooling effects. The fabric's spandex component keeps the shirt form-fitting without making it tight or restricting. And presumably whomever dons a TDU Rapid Assault shirt will become completely invisible like the model in the photo.
Rapid Assault camo sleeves are made of a tough poly/cotton ripstop and feature articulated, reinforced elbows, plus a pair of shoulder pockets for additional storage during covert ops, hand-to-hand combat, and...the paintball fights most of us will probably end up using these shirts for.