How cool of temps do you expect? I go wading for hours in the Beartooths without problems. I do carry a pair of guide pants for above 10k ft. (sometimes lower) but the light weight does not keep me warm. They supposedly breath, but you still sweat in them. If you have water on both sides of a thin piece of fabric, the heat transfer happens just as fast. You would need to wear a thermal layer under the waders. The waders only keep the thermal layer dry if you do not sweat in them. Long story short, I just wear a thermal layer like a wetsuit if I'm trying to save weight. Thermal + waders is better, but if you eat more and wear a vest (synthetic/ sleeveless for water) you may find it just as comfy. If you know someone with a freezer bag sealer, you might look into that option.