Here's the "skinny" on holsters in general, and plastic/synthetics.
The major difference between a "plastic" and a Kydex holster are, plastic holsters are usually made of nylon and are actually molded, mostly in one, seamless piece like most plastic objects are.
Kydex is a harder plastic from which holsters are made from flat sheets, much like leather holsters are.
The Kydex is cut out, bent to shape, usually riveted together along the seam, then heated and formed to fit.
As for gun wear, ALL holsters, no matter what they're made of will wear the finish.
The best liner for holsters is another, thinner piece of the same cowhide or horsehide that the rest is made from, smooth side out.
The WORST liners are the suede or soft leathers like deer skin, pig skin, or "orthopedic elk" (which isn't made from elk skin).
The softer, or sueded finishes collect dirt and grit, and literally turn into abrasive bags for the gun.
ALL holsters cause wear on the gun finish. What causes the wear is contact and friction between the gun and the holster.
The softer the liner, the more contact it makes, and the larger the area worn.
In reality, the best holsters for reduced finish wear are GOOD Kydex holsters.
These cause FASTER wear of the finish in contact areas than leather, but the wear is confined to a smaller area, and is self-limiting to those areas.
The finish will quickly be worn in contact areas, but it won't spread to other areas.
Since the plastic is much stiffer than leather, and STAYS that way, it doesn't form to the gun like leather does, so it doesn't make more and more contact as does leather when it softens with use.
A good leather holster is just about as hard as plastic, and the gun "clicks" into place. As the holster is used, it gets softer, and the leather form fits to the gun, wearing the finish.
Bottom line: All holsters will wear the finish on a gun, starting with the very first time it's inserted into the holster.
The best leather holster is either unlined at all, with a smooth finished inside, or it's lined with the same leather as the outside, with the smooth, grain side, facing the gun.
Kydex causes faster wear in contact areas, but then pretty well stops, and doesn't wear anywhere else.
The best thing you can do for finish wear is to clean the inside of the holster with a cloth and toothbrush.
Don't put ANYTHING on a leather holster, inside OR out, except a coat of neutral shoe polish on the outside.
Using any oils or dressings on a holster cause it to soften, which causes it to form to the gun more and accelerates finish wear.
Last, recognize when the holster is worn out, and retire it.
HOW a holster looks is not an indication of whether it's past it's service life.
A holster is worn out when it no longer retains the gun tightly enough to prevent the gun from moving and shifting in the holster.
Contact and friction wear gun finishes, and a used-up holster that allows the gun to move around in the holster is virtually sandpapering the gun's finish.
A worn-out holster can LOOK brand new.
It's FIT that determines service life.
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