we choose to use these shirts for our snorkeling trip to hawaii since the water is high 70's to low 80's, which can get chilly after awhile and we weren't going to deal with wetsuits and wanted a midway option - they worked great for both of us - the only thing i didn't like was that the shirt tended to ride up a bit on me but that's likely a cut issue since i'm a curvy woman wearing a man's shirt.  we definitely stayed more comfortable and also had the benefit of sun protection.