GypsyTally, I have a pair of rubber stall mucking boots (nothing special, WalMart cheap, black rubber waterproof boots) that make my feet sweat just how you're describing. I've never had a rash, though, even when I was very young and wore similar boots barefoot and in shorts, lol. I only use them to clean stalls or walk in other nasty things. I did notice, though, after I took off the leather field boots, my calves were a bit sweaty. Not soaked through the breeches or anything, just, like, they felt much cooler when I took the boots off, if that makes sense. I didn't really notice the heat or sweat when the boots were on. Granted, I was wearing black breeches and the sun was out (apparently that's how the barefoot+rubber boots compulsion manifests itself after the age of 10, lol).
A stubborn horse walks behind you, an impatient one in front of you, but a noble companion walks beside you ~ Unknown