the TRL stands for trail. the M stands for mesh. This is a no foam construction and the added 3D airmesh front panel brings a freshness to every run that you won’t ever find in a $5 truckstop trucker. all the style, none of the stink. our packable brim, reflective details, machine washable construction means that performance and protection are built right in. this cap is built using repreve, the world’s number one brand of recycled performance fiber.