Trucker caps are just another type of baseball caps. Their design is similar but usually a few panels in these caps are made of mesh. These had first evolved in the 1960s when many big companies provided these hats to truck-owners and farmers as complements for their services. Hence, the name trucker cap.
The mesh on the panels of these caps helps in providing some breathing room to the wearer. For anyone who is doing a job of hard labor, this is a great feature as it keeps them from being sweaty. Trucker caps are very popular even today.