I carry a full-size M1911 (a Kimber Classic Custom in this case) in an IWB of my own design. This holster has a flap of leather between the gun and body, and the leather is sweat-proofed with Sno Seal. I carry under a T-shirt.
This holster has the added advantage that the flap provides a place to locate a "button" (leather cam) that keeps the safety engaged while the gun's in the holster. In fact, you can take an empty, cocked and unlocked pistol, put it in the holster, and when you pull it out, it will be cocked and locked.