It is important to note that a rash guard and a compression shirt are not the same things. A compression shirt is a tight-fitting garment that provides support for the muscles and joints in the arms, chest, back, and legs. It is made from nylon or spandex fabric with stretch properties.
While a rash guard is typically made from polyester or cotton fabric with stretch properties. It provides sun protection during outdoor activities like surfing, cycling, and running while also protecting you from abrasions caused by rough surfaces like sandpaper or concrete.
The two garments have many similarities but they are not exactly the same thing.