I've used this pack on quite a few mountain biking trips now and really enjoyed having it along. The materials are lightweight and it fits comfortably on my back. Airflow on your back is pretty minimal, but I honestly haven't seen anything better out there. When its hot out I like to fill the reservoir with cold water. You get a nice cool back and cool water to drink, for a couple hours at least. Just remember to let it air out afterwards as condensation will build up inside the reservoir pocket. Speaking of which we even went through some rain and it turned out that this pack is pretty water resistant - all my stuff was dry even after being rained on for several hours.