I use pigskin to line holster.
Type of Glue: Contact Cement--coat both pieces with the contact cement, let dry till tacky, press together--I then let mine dry over-night before I sew, others here sew right away---whichever way works best for you.
Have never had to stretch it to make it fit into a fold, my holsters are flat until I wet mold them, after molding there are not wrinkles, if the glue has been correctly applied and cured.
Hope this helps.
Troy