This ship armor is derived from some of the knowledge that Selvans  gathered from his time in a wraith host. It is a standard Goa'uld hull, that has "tendrils" that grow in it. These tendrils, while not actually alive, are based off of Wraith tech. When a part of the hull takes damage, these tendrils begin to grow in that area, essentially "patching" the hull as it takes damage. As a ship gets more "patches" the hull develops a rough brown texture, that resembles the bark of a tree.