Originally Posted by vrkelley
If you already have a pack go ahead and make a tight wad of duct tape to lift the pack off your back. Attach and you've got an automatic air vent.
A good retrofit could include foam pipe insulation. It comes with a split down the length. You cut it to size with scissors, open it and lay it flat and it automotically has a springy feel, trying it go back to the pipe shape. If you duct tape this stuff, it's very close to the professionally done ones in comfort, providing you cut and position the material in the right spots.