Hello again Illflem!
I also had this concern when I ordered them from "Wetokole". I asked this question directly to the service person and she said no they are not hot or 'sweaty' like a vinyl seat. I was a bit skeptical but really wanted to give them a try. I'm happy to report that after 25,000 miles of use in 6 months that I'm still complete satisfied with their performance in my travels to Baja & Connecticut from Nashville, Tn.
I find them to be no more 'sweaty' than a normal cloth seat. I cannot compare them to leather because I have never owner a leather equipped vehicle. I have sat in them for 500 mile stints without having to peel myself off of them when finished.
My only recommendations would be to gravitate toward the darker colors for the insert colors. I have the 'mocha' & black combo and I'm beginning to show some dirt on the lighter color. We'll see how they look after their first washing.
Hope this helps..... Keeno
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1992 W250 5spd. 3. 54 gears, LSD, JRE enhanced VE Injector Pump, BD High Output Injectors, Banks "Stinger Plus" consisting of a 14cm2 wastegated housing, 3 1/2" JRE modified exhaust/muffler, pyro/boost gages, K&N, Skyjacker 2 1/2" front suspension lift to clear 305/70R/16 Goodyear MT's, Mag-Hytec, Amsoil