I never treat my IWB holsters - I don't want them soft and pliable; I prefer them to be stiff to facilitate reholstering. I find a combination of sweat and body oil is all my IWB holsters need. Over time they develop a nice patina that seems to act as a preservative, and when they get too bad (after 10 or 20 years) they get replaced. If a holster is a little too tight or squeaks a dash of talcum powder works wonders. Keep in mind it is mildly abrasive though.