I think the kydex method is to wrap the pistol in the plastic package holster came in
put the pistol in the holster, leave it in overnight, they say that will loosen it up enough
Here is a website that addresses your question
www.ballisticreview.com/glockfaq.htmlBREAKING-IN PLASTIC HOLSTERSQ. Please explain the Saran-wrap break-in for holsters.
A. I used it for the Glock plastic holster. You can use it on others of similar material.
You wrap your firearm with Saran Wrap (about 2-3 layers), then put the gun in the holster and leave it for several hours or overnight. Remove the gun and spray Armor All on the inside of the holster to slicken it up. After that dose of Armor all wore off (about 2 days), no more was needed and the gun went in and out of the holster with ease.