Well I have been carrying my Glock 30 in a fobus holster for about a year now. It is showing no signs of wear on the slide, other than a small worn spot on the slide release. Im not so sure thats the fault of the holster, since it looks like some cheap coating on it in the first place.
As for your question, no there not made out of kydex. There plastic. Howver there is somthing in the manf, process that makes it feel very smooth, almost like a swed. The holsters are great. I carry my Glock 30 in a paddle version, and my mags in a paddal version. They are light, and comfy. There is a slight bounce when runing, but when moving at a normal pace the gun is held closly to your body. They are so light the only thing you feel is the weight of the gun. Like I said it keeps the pistol tight to your side allowing you to conceal it easer. Anyone here who has used or owns a Glock 30 will tell you its a fat little gun. (it holds 10 rnds of .45ACP it has to be) and it is easly concealed in a fobus holster. Best perk about the holster is that there about 22$.
Here is a pic of my Glock 30 in its Fobus holster. Note how close it is held to my body. It is kept at my side in the FBI 45' (did I tell you that they could be adjusted too?)
http://photos.yahoo.com/bc/bullet_catcher_357/vwp?.dir=/My+pics&.src=ph&.dnm=backdrop.jpg&.view=t&.done=http%3a//photos.yahoo.com/bc/bullet_catcher_357/lst%3f%26.dir=/My%2bpics%26.src=ph%26.view=t
cut and paste the link.