I have a larger one (The Luxe) and I do sometimes notice it but that is because it has padded straps and those are what I notice. That one is the one I use for long adventures, the Rogue I even race marathons in with no complaints and I really don't notice it is there. Catrin is right too, bottles can get gunky from dirt, although with the right cage they should stay pretty secure. I use my bottle cage for something with electrolytes and water in the Camelbak. The two I posted (and it appears maybe Indy's) have a nice narrow footprint so yes you'll be sweaty but these are not your normal backpack they are made to fit your back for active adventures.