The fit is the primary distinction between a swim shirt and a rash guard. Rashguards are more like water-ready compression shirts because they are built for surfing or other high-intensity water activities. Swim shirts, on the other hand, are intended to protect against UV radiation while still being comfy. They're usually made of nylon or polyester and are designed to be worn under other clothes when going in the sun. Rash guards and swim shirts are also different in size. Rash guards are typically much smaller than swim shirts; you wouldn't wear a large rash guard unless you were swimming in extremely cold waters. On the other hand, most swim shirts are sized larger than rash guards; we recommend ordering your normal size if you're looking to protect yourself from the sun while still feeling comfortable. Finally, swim shirts don't have sleeves! This is because they're not meant to be worn by themselves but rather under something else. However, some brands do offer alternative arm coverups that can be purchased separately if desired. So, whether you're looking to protect yourself from the sun while surfing or just want to wear something fun under your regular clothes, swim shirts and rash guards are great options. They're easy to wear and look cool at the same time!