Have you tried wearing a tank top under your binder? I wear one to keep the fabric from making me itch and prevent chaffing. I've noticed the tank top absorbs the sweat first so the binder stays drier. At first I though I would get too hot wearing a tank top-binder-shirt, but it's been O.K. I'm in heat in the 90's too, but I'm not outside all day. The binder somehow has a cooling effect to it.