Hi Carissa,
I wore them last Saturday for 130 miles in 101F (at last report at 2:30 PM) heat, in Florida humidity, with no problems. It was sure fun to stick ice chunks under my toes and gloat while the others with real shoes boiled!
Seriously, I can't remember my feet ever sweating in them. I think the breeze prevents that. And, they have a snug fit, but I don't keep the straps really tight- but I just really don't feel them, either. It's like I'm just stepping on soft rubber platforms. But I think I have an efficient pedal stroke, still.
Their first ride was Three State Three Mountain. Not horribly hot, but 105 miles with MAJOR climbing. And 1/4 mile of walking! :-) (22% grade!)
Nanci
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"...I'm like the cycling version of the guy in Flowers for Algernon." Mike Magnuson