Alright, kind of a stupid question, but looking for input anyways. I've been training for a SOBO thru-hike this year and have been using some kind of Osprey internal frame pack (not sure of the name) with 30lbs of weights. This weekend I packed up all of my gear and some food (roughly 24lbs) and did an over-nighter with a different pack. I got a crazy heat rash where the straps were. Now, considering I was carrying a lighter load, this kind of shocked me; however, most of my training hikes are roughly 10miles a clip, vs almost 30miles in 2 days this past weekend. I did a 22mile hike 2 weeks ago (with the osprey), but was only carrying about 15lbs and had no problems with the rash. So, I'm curious if you guys think this is due to the pack being on longer or a change in the pack dynamics (foam strapping, breathability, fit, etc). Has anyone had a similar experience? I'm curious if I need to test some extra padding with this pack, check fitting, or search for something new. The pack I'm using is the HMG windrider southwest.