As the others have said, non-porous materials will moisture repellant, but not nearly as comfortable. Like most here, I have quite a varitey of materials and manufactures, and everything is a compromise. I prefer leather for IWB, for comfort reasons, but finding the perfect holster for you may take a few purchases, or lifetime, to achieve.
When considering a holster I would make sure that it has a sweat guard/full coverage against direct HG contact. Horsehide, though not quite a pliable as regular leather, is far more mositure resistant, and worth the price difference. Leather adds bulk as you know, so for IWB I'm a big fan of
www.crossbreedholsters.com, which blends the comfort of leather with kydex to make one comfortable tuckable IWB.