Another who enjoys wearing man-made plant fiber materials (for me that's rayon, viscose, and lyocell/tencel/cupro). I find viscose plenty breathable in hot weather; in fact I look for it in my jersey knits, if possible. Rayon blends (cotton, linen, or silk) are especially lovely feeling! And tencel is my favorite of all, natural fibers included. I will say that I do find viscose (and some rayons to a lesser extent) a little finicky for washing though, especially wovens. I tend to take mine to the dry cleaners because I've shrunken several pieces doing simple hand washing at home.