Leathe LOL you will die die die in the heat. All nice and comfy when you are moving but if you live like where I do and have only one traffic light jk.. when you stop at a red you will boil and bake ache and sweat. Think about this...cool bike, cool leather jacket, hot day cute chick, all sweaty, and persperation under arm pits. Makes no sense. Get a jacket that comes with a liner that can be removed. I believe AGV makes a good HYBRID with leather on the area most likely to touch and scrape/ mesh material in low impact areas. I had the first one of the hybrid AGV's and it was great. When it rained or was cold I put the liner on and was fine. Sweat sucks dude, and it causes fatigue on longer rides.