If you are looking for an upper that offers lots of ventilation, comes with a lot of pockets, and features reflective details then Nylon 150's is the best material to go with. You can also find cotton fabrics during the summer months but make sure your lower doesn't feel too warm so stay at or below 30 degrees Fahrenheit for that particular area. Cotton fabric does not breathe well in hot environments like higher temperatures tend to lock up perspiration inside very fast.